12,570 results for Doctoral

  • Characterization of ORFV119

    Harfoot, Rhodri Thomas (2015)

    Doctoral thesis
    University of Otago

    A large number of viruses are known to produce proteins that interact with pRB. For the most part these are small DNA viruses, such as Adenovirus and Human papilloma virus, which require that the cell be in a replicative state itself before they can replicate themselves. For this purpose, these viruses produce proteins (E1A and E7 respectively) that bind to pRB and disrupt its interaction with E2F family members, thereby pushing the cells into the synthesis phase of the cell cycle, and enabling the virus to utilize the resources that the cell generates for replication. At this point, the invading virus co-opts the host-cell replication machinery to replicate the viral genome and produce the protein coat. Poxviruses complete their replication cycle in the cytoplasm rather than the nucleus, and encode much of their own replication machinery, and as such were, until recently not thought to co-opt host cellular replicative mechanisms. Moreover, until recently, poxviruses were also not thought to alter the cell cycle extensively. Based on these concepts, it seemed unlikely that poxviruses would encode a putative pRB binding protein. This thesis aimed to identify and characterize a novel pRB binding protein from orf virus (ORFV), known as ORFV119. Bioinformatics analyses predicted that, the ORFV119 protein contained two putative functional motifs, a pRB binding motif (LXCXE) in the C terminus and a mitochondrial targeting motif in the N terminus. These motifs both matched closely those found in other proteins known to contain the respective motifs. It was found that ORFV119 was completely conserved within isolates orf virus, and homologues were present in other species within the Parapoxvirus genus, but largely absent outside this clade, apart from in Molluscipoxvirus. ORFV119 was determined to be an early gene by detection of the protein 8 hours post infection using an antiserum against ORFV119 developed during this thesis. The protein was detected as a punctate staining in the cytoplasm, that co-localized with mitochondria. In the absence of the putative mitochondrial targeting motif, the staining was dispersed throughout the cell with occasionally enhanced signal in the nucleus. A construct expressing only the predicted pRB binding motif fused to GFP showed a similar pattern to that seen for constructs where the mitochondrial targeting motif had been removed. A construct which had had the LXCXE domain removed showed staining similar to full-length protein. Co-immunoprecipitation showed that full-length ORFV119 was capable of binding to, and co-precipitating pRB, and that this was dependent on the presence of the LXCXE motif, indicating that ORFV119 does bind to pRB through a canonical mechanism. Luciferase assays for E2F responsive promoter activity found that ORFV is capable of a mild activation of E2F responsive promoters. Full length ORFV119 was also able to stimulate E2F responsive promoter activity. The same assays performed using ORFV119 truncations showed that upon removal of the LXCXE motif, ORFV119 was still capable of activating E2F responsive promoters, but removal of the mitochondrial targeting motif removed this ability. It is postulated that this is due to the structure of ORFV119 and its respective truncation mutants, where ORFV119 and the delta-LXCXE mutants both had structures similar to pRB, whereas the delta-Mito did not, thus it could be that ORFV119 is mimicking pRB and competing with pRB for E2F. A Molluscum contagiosum virus (MOCV) protein with a similar range of properties has been identified (Mohr et al., 2008). Phylogenetic comparison of the ORFV and MOCV proteins indicates low sequence similarity and identity, despite overall similarities in protein size and positions of the motifs. This indicates that it is unlikely that the two proteins are related, but rather a common solution to a common problem. In summary, this is the first report of a novel pRB binding and mitochondrial targeting protein from orf virus, which may enable the virus to create a cellular environment conducive for viral replication.

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  • Health in late prehistoric Thailand

    Domett, Kathryn M. (1999)

    Doctoral thesis
    University of Otago

    xvii, 326 leaves :ill. (some col.), col. maps, form ; 30 cm. Includes bibliographical references.

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  • Synthesis and Reactivity of Transition Metal Complexes of Polypyridyl Ligands

    Lo, Warrick Ken Cheung (2015)

    Doctoral thesis
    University of Otago

    The work presented in this thesis was conducted with the aim of developing new polypyridyl based ligands, establishing coordination chemistry of their metal (mainly d6 and d8) complexes and studying the reactivities of these complexes for a range of potential applications. Chapter 1 introduces the field of coordination chemistry and metal complexes. A brief overview on some key concepts in structural constitution, geometry, stability and reaction mechanism of metal complexes is provided. In addition, the advantages of employing pyridyl based ligands in the development of functionalised metal complexes are discussed. Recent literature examples of metal complexes of multidentate polypyridyl based ligands and their applications are given. Roles of polypyridyl based ligands in these complexes are also discussed. Chapter 2 presents the study of the reactivities of [Pt(diimine)2]2+ (diimine = 2,2′-bipyridine (bpy) and 4,4′-dimethyl-2,2′-bipyridine (4,4′-Me2bpy)) towards a range of monodentate ligands (pyridine and phosphine). Reaction intermediates and products of these reactions were characterised by spectroscopic techniques and, in some cases, X-ray crystallography. NMR studies showed that reaction of [Pt(bpy)2]2+ and one equivalent of pyridine or substituted pyridines gave multiple products (free bpy ligands and [Pt(bpy)(pyridine)2]2+) whereas analogous reactions with phosphine ligands gave solely the long-lived five-coordinate intermediates [Pt(diimine)2(phosphine)]n+. Reaction of [Pt(diimine)2]2+ with an excess amount of phosphine ligands gave the four-coordinate products [Pt(diimine)(phosphine)2]2+. Isolation and characterisation by X-ray crystallography of one of these intermediates provide definitive structure evidence that reaction of [Pt(diimine)2]2+ and phosphine ligands proceeds via the associative ligand substitution mechanism. Chapter 3 examines the synthesis and properties of inverse and regular 2-pyridyl-1,2,3-triazole complexes of Pd(II), Pt(II), Re(I) and Ru(II). A comparison of the structures, stability, photochemical, electrochemical and photophysical properties of the d6 and d8 metal complexes shows that despite the inverse and regular triazole complexes are structurally very similar, their chemical and physical properties are quite different. The stability of these complexes was examined by ligand exchange studies, solution stability studies and DFT calculations. These studies showed that inverse triazole ligands formed less stable complexes than the isomeric regular triazole ligands. In addition, inverse [Ru(bpy)2(triazole)]n+ complexes are photochemically active upon UV light irradiation, whereas regular [Ru(bpy)2(triazole)]n+ complexes are photochemically inert under identical conditions. Electronic properties of inverse triazole complexes have been examined using cyclic voltammetry, electronic absorption and emission spectroscopies and DFT calculations and were shown to be quite different from the regular triazole complexes. Chapter 4 describes a new purification procedure for the widely used pentadentate polypyridyl ligand N4Py and the synthesis of a family of [CoIII(N4Py)(X)]n+ complexes. Cyclic voltammetry and electronic absorption spectroscopic studies showed that electronic properties of [CoIII(N4Py)(X)]n+ complexes could be tuned by varying the nature of monodentate ligand X. Photocatalytic hydrogen production studies in aqueous solutions showed that all six tested [CoIII(N4Py)(X)]n+ complexes are catalysts for hydrogen production from water and displayed relative low catalytic activities, when compared to cobalt polypyridyl complexes reported in the literature. Results from a preliminary mechanistic study are also discussed. Chapter 5 describes the synthesis of a new quinolinyl based ligand 2PyN2Q, derived from N4Py, and the synthesis of octahedral zinc and copper complexes of 2PyN2Q and N4Py. The coordination chemistry of 2PyN2Q is compared to that of N4Py. Consequences of replacing two pyridyl groups in N4Py with two sterically bulky and more electronic withdrawing quinolinyl groups for the structures and electronic properties of metal 2PyN2Q complexes were examined by X-ray crystallography, cyclic voltammetry and electronic absorption spectroscopy.

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  • Digital Holographic Interferometry for Radiation Dosimetry

    Cavan, Alicia Emily (2015)

    Doctoral thesis
    University of Canterbury Library

    A novel optical calorimetry approach is proposed for the dosimetry of therapeutic radiation, based on the optical technique of Digital Holographic Interferometry (DHI). This detector determines the radiation absorbed dose to water by measurement of the refractive index variations arising from radiation induced temperature increases. The output consists of a time series of high resolution, two dimensional images of the spatial distribution of the projected dose map across the water sample. This absorbed dose to water is measured directly, independently of radiation type, dose rate and energy, and without perturbation of the beam. These are key features which make DHI a promising technique for radiation dosimetry. A prototype DHI detector was developed, with the aim of providing proof-of-principle of the approach. The detector consists of an optical laser interferometer based on a lensless Fourier transform digital holography (LFTDH) system, and the associated mathematical reconstruction of the absorbed dose. The conceptual basis was introduced, and a full framework was established for the measurement and analysis of the results. Methods were developed for mathematical correction of the distortions introduced by heat di usion within the system. Pilot studies of the dosimetry of a high dose rate Ir-192 brachytherapy source and a small eld proton beam were conducted in order to investigate the dosimetric potential of the technique. Results were validated against independent models of the expected radiation dose distributions. Initial measurements of absorbed dose demonstrated the ability of the DHI detector to resolve the minuscule temperature changes produced by radiation in water to within experimental uncertainty. Spatial resolution of approximately 0.03 mm/pixel was achieved, and the dose distribution around the brachytherapy source was accurately measured for short irradiation times, to within the experimental uncertainty. The experimental noise for the prototype detector was relatively large and combined with the occurrence of heat di usion, means that the method is predominantly suitable for high dose rate applications. The initial proof-of-principle results con rm that DHI dosimetry is a promising technique, with a range of potential bene ts. Further development of the technique is warranted, to improve on the limitations of the current prototype. A comprehensive analysis of the system was conducted to determine key requirements for future development of the DHI detector to be a useful contribution to the dosimetric toolbox of a range of current and emerging applications. The sources of measurement uncertainty are considered, and methods suggested to mitigate these. Improvement of the signal-to-noise ratio, and further development of the heat transport corrections for high dose gradient regions are key areas of focus highlighted for future development.

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  • Late Transition Metal Complexes of Pyridyldiphosphines

    Vaughan, Teresa Florence (2015)

    Doctoral thesis
    Victoria University of Wellington

    This thesis provides an account of research into the properties of pyridyldiphosphines with o-xylene and m-xylene backbones. The coordination behaviour of the o-xylene based ligand with platinum, palladium, silver, rhodium and iridium metal centres has been studied, with an emphasis on whether the presence of the pyridyl rings affects the products formed. Platinum and palladium pincer complexes have been synthesised and the intermediates investigated. The formation of trimetallic complexes with these ligands acting as bridging ligands has also been explored. Two new pyridyldiphosphines, o-C₆H₄(CH₂PPy₂)₂ (3) and m-C₆H₄(CH₂PPy₂)₂ (4), and one known pyridyldiphosphine, PPy₂(CH₂)₃PPy₂ (5), have been synthesised via an improved method. Tris(2-pyridyl)phopshine was reacted with a lithium dispersion to give LiPPy₂, which was then reacted with the appropriate dichloride or dibromide compound to yield the desired ligand. The phosphine selenides of 3 and 4 were synthesised and the ¹J PSe values of 738 and 742 Hz indicated these ligands were less basic than PPh₃. While the ligands themselves were not water-soluble, protonation by a strong acid, such as HCl or H₂C(SO₂CF₃)₃, rendered them soluble in water. A series of [MX₂(PP)] complexes (where M = Pt, X = Cl, I, Me, Et, PP = 3, 5; M = Pd, X = Cl, Me PP = 3, 5) were synthesised. Complexes of 3 displayed dynamic behaviour in solution which was attributed to the backbone of the ligand inverting. When [PtMeCl(PP)] (27) was reacted with NaCH(SO₂CF₃)₂ no evidence for the coordination of the pyridyl nitrogens was observed. The synthesis of a series of unsymetrical [PtMeL(PP)]⁺ complexes enabled the comparison of the cis and trans influences of a range of ligands. The following cis influence series was compiled based on ³¹P NMR data of these complexes: Py ≈ Cl > SEt₂ > PTA > PPh₃. Reaction of 27 with NaCH(SO₂CF₃)₂ and carbon monoxide slowly formed an acyl complex, where the CO had inserted in the Pt–Me bond. The bis-chelated complexes [M(PP)₂] where M = Pt, Pd, and [Ag(PP)₂]⁺ were formed. In these complexes 3 acted as a diphosphine ligand and there was no evidence for any interaction between the pyridyl nitrogen atoms and the metal centre. Reaction of 3 with [Ir(COD)(μ-Cl)]₂ formed [IrCl(PP)(COD)] (42). When the chloride ligand in 42 was abstracted, the pyridyl nitrogens were able to interact with the iridium centre faciliating the isomerisation of the 1,2,5,6-ƞ⁴-COD ligand to a 1-к-4,5,6-ƞ³-C₈H₁₂ ligand. The X-ray crystal structure of [Ir(1-к-4,5,6-ƞ³-C₈H₁₂)(PPN)]BPh₄ (43) confirmed the P,P,N chelation mode of the ligand. In solution, 43 displayed hemilabile behaviour, with the pyridyl nitrogens exchanging at a rate faster than the NMR time scale at room temperature. The coordinated pyridyl nitrogen was able to be displaced by carbon monoxide to form [Ir(1-к-4,5,6-ƞ³-C₈H₁₂)(CO)(PP)]⁺. A series of [PtXY(μ-PP)]₂ complexes, where X = Y = Cl, Me, X = Cl, Y = Me and PP = 4, were formed initially when 4 was reacted with platinum(II) complexes. When heated, the dimers containing methyl ligands eliminated methane to form [PtX(PCP)] pincer complexes, X = Cl (49), Me (51). When the chloride ligand in 49 was abstracted no evidence of pyridyl nitrogen coordination was observed. Protonation of 49 did not yield a water-soluble pincer complex. The [PdCl₂(μ-PP)]₂ complex readily metallated when heated to give the pincer complex [PdCl(PCP)]. Given pyridyl nitrogen atoms are known to be good ligands for “hard” metal centres, the ability of the pyridyl nitrogens in 3 and 4 to coordinate to metal centres was investigated. While complexes with chloride ligands were found to form insoluble products, the synthesis of [(PtMe₂)₃(PP)], from the reaction of either 3 or [PtMe₂(PP)] (17) with dimethyl(hexa-1,5-diene)platinum, proceeded smoothly through a dimetallic intermediate. The same reactivity was observed in the synthesis of [(PtMe₂)₂PtMe(PCP)]. In contrast, the cationic heterotrimetallic complexes [{M(COD)}₂PtMe(PP)]²⁺ and [{M(COD)}₂PtMe(PCP)]²⁺, where M = Rh or Ir, were synthesised without the detection of any intermediates. However, dimetallic complexes were formed as part of a mixture when 17 or 51 was reacted with one equivalent of the appropriate metal complex.

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  • Identification of fall-risk factor degradations using quality of balance measurements

    Bassement, Jennifer

    Doctoral thesis
    Auckland University of Technology

    Falls concern a third of the people aged over 65y and lead to the loss of functional ability. The detection of risks factors of falls is essential for early interven- tion. Six intrinsic risk factors of fall: vision, vestibular system, joint range of motion, leg muscle strength, joint proprioception and foot cutaneous propriocep- tion were assessed with clinical tests before and after temporarily degradation. Standing balance was recorded on a force plate. From the force plate, 198 parameters of the centre of pressure displacement were computed. The parame- ters were used as variables to build neural network and logistic regression model for discriminating conditions. Feature selection analysis was per- formed to reduce the number of variables. Several models were built including 3 to 10 condi- tions. Models with 5 or less conditions appeared acceptable but better performance was found with models including 3 conditions. The best accuracy was 92% for a model including ankle range of motion, fatigue and vision contrast conditions. Qualities of balance parameters were able to diag- nose impairments. However, the efficient models included only a few conditions. Models with more conditions could be built but would require a larger number of cases to reach high accuracy. The study showed that a neural network or a logistic model could be used for the diagnosis of balance impairments. Such a tool could seriously improve the prevention and rehabilitation practice.

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  • Quantifying Spatial and Temporal Deposition of Atmospheric Pollutants in Runoff from Different Pavement Types

    Murphy, Louise Una (2015)

    Doctoral thesis
    University of Canterbury Library

    Urban development leads to increased impermeable landscapes that interrupt the hydrological cycle by creating an impermeable barrier to the natural infiltration of precipitation. Precipitate, unable to infiltrate, flows over impermeable surfaces as sheet runoff, carrying the pollutants from the land with it; thus comprising the quality of the stormwater. The runoff is redirected (frequently untreated) to nearby waterways altering their water quality and quantity, thereby, adversely affecting receiving aquatic ecosystems. Suspended solids and elevated heavy metal concentrations in stormwater are the leading causes of water quality degradation in urban waterways in New Zealand. It is widely reported that vehicles and metal roofs are a major direct source of the key pollutants (total suspended solids (TSS) and heavy metals) in stormwater runoff; however, the contribution of atmospheric deposition, as an indirect source, in stormwater runoff is rarely considered. This is principally due to the many uncertainties and challenges with measuring and managing these pollutants in stormwater runoff. Therefore, a monitoring programme into the dynamics controlling atmospherically derived pollutant build-up and wash-off from urban surfaces was conducted. In particular, this research focused on the spatial and temporal variability of Cu, Zn, Pb, and TSS deposition in different land-use areas; the influence of pavement type on atmospherically-deposited pollutant loads in stormwater; and the contribution of wet deposition and dry deposition to the total deposition loads. Impermeable concrete boards (≈ 1 m2) were deployed for 11 months in different land-use areas (industrial, residential and airside) in Christchurch, New Zealand, to capture spatially distributed atmospheric deposition loads in runoff over varying meteorological conditions. Mixed-effect regression models were developed to explain the influence of different meteorological characteristics on pollutant build-up and wash-off dynamics. Next, impermeable asphalt, permeable asphalt, impermeable concrete, and permeable concrete boards were deployed for two months in a residential land-use area to determine the influence of pavement composition and roughness on pollutant loads in stormwater. Finally, wet deposition samples were analysed in an industrial land-use area for 8 months to monitor the contribution of wet deposition to atmospherically-deposited pollutant loads. All samples were analysed for total and dissolved Cu, Zn, Pb, and TSS. Pavement type: Results showed that both impermeable and permeable concrete were efficient at retaining Cu and Zn. Bitumen leaching from the impermeable asphalt was a significant source of Zn to runoff. However, bitumen leaching from the permeable asphalt did not contain elevated Zn loads. Infiltrate from the permeable asphalt provided little/no removal of Cu and Zn. Impermeable asphalt provided greater retention of TSS and Pb over impermeable concrete because its rougher surface entrapped more particulates. TSS and Pb loads were the lowest from the permeable pavements due to the pavers filtering out particulates. Spatial variability: Results showed that all three land-use areas exhibited similar patterns of varying metal and TSS loads, indicating that atmospherically-deposited metals and TSS had a homogenous distribution within the Christchurch airshed. This suggested that the pollutants originated from a similar source and that the surrounding land-use was not an important factor in determining atmospheric pollutant loads to stormwater runoff. Although, higher pollutant loads were found for the industrial area, this was attributed to local topographic conditions rather than land-use activity. Temporal variability: Results illustrated the importance of antecedent dry days on pollutant build-up. Peak rainfall intensity and rain duration had a significant relationship with TSS and Pb wash-off; rain depth had a significant relationship with Cu and Zn wash-off. This suggested that the pollutant speciation phase plays an important role in surface wash-off. Rain intensity and duration influenced particulate pollutants, whereas, rain depth influenced dissolved pollutants. Additionally, mixed-effect models could predict approximately 53-69% of the variation in airborne pollutant loads in runoff. Deposition pathways: Wet deposition was an important contributor of dissolved Zn to stormwater runoff. However, dry deposition was the greatest source of total Cu, Zn, and Pb loads in stormwater runoff. This is principally due to the low annual rainfall in Christchurch limiting pollutant removal via wet deposition unlike dry deposition, which is continually occurring. Understanding the dynamics of airborne pollutant deposition and their contribution to stormwater pollution could help stormwater managers in strategic decision-making processes such as choice of location and installation of different treatment systems.

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  • Dynamic behaviour of brain and surrogate materials under ballistic impact

    Soltanipour Lazarjan, Milad (2015)

    Doctoral thesis
    University of Canterbury Library

    In the last several decades the number of the fatalities related to criminally inflicted cranial gunshot wounds has increased (Aarabi et al.; Jena et al., 2014; Mota et al., 2003). Back-spattered bloodstain patterns are often important in investigations of cranial gunshot fatalities, particularly when there is a doubt whether the death is suicide or homicide. Back-spatter is the projection of blood and tissue back toward the firearm. However, the mechanism of creation of the backspatter is not understood well. There are several hypotheses, which describe the formation of the backspatter. However, as it is difficult to study the internal mechanics of formation of the backspatter in animal experiments as the head is opaque and sample properties vary from animal to animal. Performing ballistic experiments on human cadavers is rarely not possible for ethical reasons. An alternative is to build a realistic physical 3D model of the human head, which can be used for reconstruction of crime scenes and BPA training purposes. This requires a simulant material for each layer of the human head. In order to build a realistic model of human head, it is necessary to understand the effect of the each layer of the human head to the generation of the back-spatter. Simulant materials offer the possibility of safe, well‐controlled experiments. Suitable simulants must be biologically inert, be stable over some reasonable shelf‐life, and respond to ballistic penetration in the same way as the responding human tissues. Traditionally 10-20% (w/w) gelatine have been used as a simulant for human soft tissues in ballistic experiments. However, 10-20% of gelatine has never been validated as a brain simulant. Moreover, due to the viscoelastic nature of the brain it is not possible to find the exact mechanical properties of the brain at ballistic strain rates. Therefore, in this study several experiments were designed to obtain qualitative and quantitative data using high speed cameras to compare different concentrations of gelatine and new composite material with the bovine and ovine brains. Factors such as the form of the fragmentation, velocity of the ejected material, expansion rate, stopping distance, absorption of kinetic energy and effect of the suction as well as ejection of the air from the wound cavity and its involvement in the generation of the backspatter have been investigated. Furthermore, in this study a new composite material has been developed, which is able to create more realistic form of the fragmentation and expansion rate compared to the all different percentage of the gelatine. The results of this study suggested that none of the concentrations the gelatine used in this study were capable of recreating the form of the damage to the one observed from bovine and ovine brain. The elastic response of the brain tissue is much lower that observed in gelatine samples. None of the simulants reproduced the stopping distance or form of the damage seen in bovine brain. Suction and ejection of the air as a result of creation of the temporary cavity has a direct relation to the elasticity of the material. For example, by reducing the percentage of the gelatine the velocity of the air drawn into the cavity increases however, the reverse scenario can be seen for the ejection of the air. This study showed that elastic response of the brain tissue was not enough to eject the brain and biological materials out of the cranium. However, the intracranial pressure raises as the projectile passes through the head. This pressure has the potential of ejecting the brain and biological material backward and create back-spatter. Finally, the results of this study suggested that for each specific type of experiment, a unique simulant must be designed to meet the requirements for that particular experiment.

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  • Critical success factors for outsourced software development projects from a vendor's perspective: A structural equation modelling analysis of traditional plan-based and agile methodologies

    Ahimbisibwe, Arthur (2015)

    Doctoral thesis
    Victoria University of Wellington

    There are many factors proposed as to why software projects fail, one of them is the inappropriate choice of a project management methodology. Although there is an increased range of available management choices, project managers do not frequently consider their alternatives. They tend to narrowly tailor project categorisation systems and use categorisation criteria that are not logically linked with objectives. To address this, this study develops and tests an integrative contingency fit model for contrasting perspectives of traditional plan-based and agile methodologies specifically for outsourced software development projects. In addition, it takes a vendor‘s perspective, rather than the client perspective that is mostly used. Overall, the research seeks to answer these questions: (RQ1) what are the Critical Success Factors (CSFs) for outsourced software development projects from a vendor‟s perspective? (RQ2) What are the differences in these CSFs for traditional plan-driven and agile methodologies towards project success from a vendor‟s perspective? The IT literature reveals two major distinct categories of methodologies: traditional plan-based and agile. Previous research has identified CSFs with respect to project success with mixed findings. The recent increase in popularity of methodologies has shifted the debate, interest and controversy to CSFs that are the factors which are most important to make a methodology successful. While there is an increasing diversity of project types, project contexts and methodologies, the frameworks or theories connecting these are limited. To date software development projects studies have addressed generally one methodology per study and perceived candidate CSFs as a form of reasons of success amidst a wide range of project success criteria. Although contingency theory has been previously argued for outsourced software development projects, empirical models have frequently not fully incorporated contingency as fit or fit as moderation (i.e. traditional vs. agile). This study sought to fill this research gap. Cross-sectional data from 984 senior vendor project managers and team leaders was collected by a global web-based survey. Structural Equation Modelling (SEM) (a multivariate statistical technique, in which parameters are estimated by minimizing the discrepancy between the model-implied covariance matrix and the observed covariance matrix) was used for data analysis. SEM results provide support for several contingency hypotheses theorizing relationships between candidate CSFs and project success. Project management methodology was found to moderate the effects of various CSFs on project success, and in different ways for various success measures. Similarly, the results show the level of project uncertainty moderates the impact of various CSFs on project success, and in different ways for various success measures. Together these findings provide empirical support for contingency as fit and more fully incorporate fit as moderation. The study contributes towards understanding the differences between traditional plan-based and agile project management based on the perceptions of vendor respondents with regard to their client organizations, and also to understanding what are the most significant antecedents of success (the CSFs) in different project contexts. The study also examines the indirect and interaction effects, and the findings contribute towards understanding of the contingency perspective as a framework to be used by project managers and organizations. Practical implications of these results suggest that project managers should tailor project management methodologies according to various project types, which is likely to improve current project success rates.

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  • Inverse problems in astronomical imaging

    Johnston, Rachel Anne (2000)

    Doctoral thesis
    University of Canterbury Library

    The imaging of astronomical objects is limited by atmospheric turbulence, which consists of layers of varying refractive index surrounding the earth. These refractive index fluctuations are a direct consequence of the warming and cooling of air and water vapour in the atmosphere. Wavefronts entering the atmosphere acquire phase distortions, which when propagated result in amplitude fluctuations known as scintillation. Hence the practical manifestation of the atmosphere is a degradation of the signals passing through it, for example it severely limits the resolution of images captured by ground-based telescopes. A variety of solutions, or inverse problems, have been proposed and trialed in the attempt to obtain the best possible images from astronomical telescopes. An orbiting telescope (for example the Hubble space telescope) is one solution. In this case light is captured before it is distorted by the atmosphere. Less expensive ground-based solutions include the post processing of short exposure images and real-time compensation using adaptive optics, both of which are investigated in this thesis. However, the success of an inverse problem lies in the accurate modelling of the processes that give rise to the corresponding forward problem, in this case the random refractive index fluctuations that characterise the atmosphere. Numerical simulation of atmospheric turbulence is achieved using phase screens in which the assumption of Kolmogorov statistics is often made. A previously presented method for modelling Kolmogorov phase fluctuations over a finite aperture, the midpoint displacement method, is both formalised and improved. This enables the accurate generation of atmospheric speckle images for the development and testing of post processing methods. Another aspect of the forward problem is the accurate simulation of scintillation, resulting from the propagation of phase distorted wavefronts. Commonly used simulation methods achieve this by assuming periodic boundary conditions. A technique for the accurate modelling and simulation of scintillation from an aperiodic Kolmogorov phase screen is presented. The more physically justifiable assumption of smoothness is shown to result in a propagation kernel of finite extent. This allows the phase screen dimensions for an accurate simulation to be determined and truncation can then be used to eliminate the unwanted spectral leakage and diffraction effects usually inherent in the use of finite apertures. Deconvolution methods are popular for the post processing of atmospheric speckle images to compensate for the effects of the atmosphere. Conventional deconvolution algorithms are applied when the distortion is known or well-characterised, whereas, blind deconvolution algorithms are used when the distortion is unknown. Conventional deconvolution techniques are not often directly applied to astronomical imaging problems as the distortion introduced by the atmosphere is unknown. However, their extension to blind deconvolution is straightforward and hence their development is valuable. The ill-conditioning of the deconvolution problem requires the addition of prior information, such as positivity, to enable its solution. It is shown that the conventional deconvolution problem can be reformulated as an equivalent quadratic programming problem. Consequently, an accelerated quadratic programming approach is applied and shown to be an improvement to an existing method used for enforcing positivity in deconvolution applications. The main algorithmic differences of the new method are implementation via the fast Fourier transform (FFT) and guaranteed convergence to the constrained minimum. Blind deconvolution is also an interesting problem that may arise in many fields of research. It is of particular relevance to imaging through turbulence where the point spread function can only be modelled statistically, and direct measurement may be difficult. The extension of the quadratic programming method to blind deconvolution, combined with Tikhonov-Miller regularisation (energy constraints), smoothness constraints, penalty terms and statistical priors produced a series of new algorithms. The performance of these algorithms is illustrated on simulated astronomical speckle images. Ground-based adaptive optics (AO) technologies are an alternative to post processing methods and aim to compensate for the distortion introduced by the atmosphere in real-time. Knowledge of the vertical structure of the atmosphere combined with AO provides the potential for compensation over a wide field of view. However, the continually changing nature of atmospheric turbulence places strict requirements on techniques for determining the turbulence structure. The remote sensing of scintillation data to estimate this information is known as scintillation detection and ranging (SCIDAR). Application of SCIDAR methods to the capture and analysis of experimental data, as demonstrated in this thesis, highlighted a number of problems with the technique. Methods for overcoming these difficulties are discussed and demonstrated. Finally, alternative approaches to the estimation of atmospheric turbulence profiles and a proposed new technique are investigated.

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  • The chemistry of the bioluminescence of the New Zealand Glow-Worm

    Watkins, Oliver (2016)

    Doctoral thesis
    University of Otago

    The aim of the research described in this thesis was to discover the luciferin responsible for bioluminescence in the New Zealand glow-worm (GW) Arachnocampa luminosa. This work was done in partnership with Dr Miriam Sharpe whose focus was to elucidate the luciferase. In order to determine the structure of the GW luciferin, the luciferin had to be isolated from the GW and the structure elucidated via characterisation. However, luciferin purifications pose a unique isolation challenge, combining the difficulties of isolating material from source organisms, working with unstable materials, and working with enzymatic assays. Furthermore characterisation of luciferins is often difficult due to the small amounts that can be isolated and because luciferins are often highly unstable. Previous work on luciferins in other organisms and on the GW luciferin is reveiwed in Chapter 1. Chapter 1 also reviews the general literature on bioluminescence but with a focus on luciferins rather than luciferases. Chapters 2 describes the collection of Arachnocampa luminosa from the wild, and the development of a GW bioluminescence assay that enabled GW luminescent molecules to be detected. This assay enabled the detection of two different types of luminescence: P type luminescence and L type luminescence. Chapter 3 describes the separation of glow-worm lysates by reverse phase chromatography and how the luminescence assay was used to trace GW luminescent molecules through the purification process. This led to the discovery of two glow-worm luciferin precursors: tyrosine and xanthurenic acid that gave P type luminescence with the GW bioluminescence assay. The compound responsible for the L type luminescence was separated away from the compounds responsible for P type luminescence but could not be isolated. The compound responsible for L type luminescence was found to co-elute with tryptophan and is thought to be the GW luciferin. Chapter 4 describes how commercial samples of these precursors (xanthurenic acid and tyrosine), along with GW enzymes, were used to produce a compound (LRPA) that could be characterised by MS and 1H NMR. A solution of LRPA was found to produce L type luminescence with the luminescence assay showing LRPA to be either the GW luciferin or a closely related compound. Chapter 5 then describes the synthesis of two molecules (N-carbamyl tyrosine and phenol-O-carbamyl tyrosine) that were candidates for a compound that co-eluted with tyrosine. Neither of these molecules matched the unknown candidate which was later found to be 3-OH kynurenine. The research on the New Zealand glow-worm described in this thesis required intensive use of LC-MS techniques. However the research was often slowed by a shortage of glow-worms. These techniques were therefore used to investigate another New Zealand natural products problem involving insect metabolites; the origins of tutin, hyenanchin and the tutin glucosides found in New Zealand toxic honeys. Chapter 6 therefore describes a quantitative LC-MS study that shows that these compounds are of plant, not insect origin and that tutu may use glycosylation to aid in tutu transport.

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  • The Numerical Initial Boundary Value Problem for the Generalised Conformal Field Equations in General Relativity

    Stevens, Christopher Zane (2016)

    Doctoral thesis
    University of Otago

    The purpose of this work is to develop for the first time a general framework for the Initial Boundary Value Problem (IBVP) of the Generalised Conformal Field Equations (GCFE). At present the only investigation toward obtaining such a framework was given in the mid 90's by Friedrich at an analytical level and is only valid for Anti-de Sitter space-time. There have so far been no numerical explorations into the validity of building such a framework. The GCFE system is derived in the space-spinor formalism and Newman and Penrose's eth-calculus is imposed to obtain proper spin-weighted equations. These are then rigorously tested both analytically and numerically to confirm their correctness. The global structure of the Schwarzschild, Schwarzschild-de Sitter and Schwarzschild-Anti-de Sitter space-times are numerically reproduced from an IVP and for the first time, numerical simulations that incorporate both the singularity and the conformal boundary are presented. A framework for the IBVP is then given, where the boundaries are chosen as arbitrary time-like conformal geodesics and where the constraints propagate on (at least) the numerical level. The full generality of the framework is verified numerically for gravitational perturbations of Minkowski and Schwarzschild space-times. A spin-frame adapted to the geometry of future null infinity is developed and the expressions for the Bondi-mass and the Bondi-time given by Penrose and Rindler are generalised. The Bondi-mass is found to equate to the Schwarzschild-mass for the standard Schwarzschild space-time and the famous Bondi-Sachs mass loss is reproduced for the gravitationally perturbed case.

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  • What Happened at the End of Lapita: Lapita to Post-Lapita Pottery Transition in West New Britain, Papua New Guinea

    Wu, Pei-hua (2016)

    Doctoral thesis
    University of Otago

    This study presents a detailed Lapita to Post-Lapita sequence/transition with chronology at particular sites in west New Britain, through the medium of pottery analysis of style and production. The data allow me to address the research questions: (1) the cultural change that happened toward the end of Lapita, and (2) the issue of cultural continuity/discontinuity between the Lapita and Post-Lapita periods. This study identified a cultural change with greater break down and regionalization/diversification of the Lapita societies in the Late Lapita phase around and after 2750/2700 BP. This study also identified detailed pottery characterization, production, and provenance in west New Britain through compositional analysis, using a scanning electron microscope (SEM), which helps in understanding the interactions in the Lapita and Post-Lapita periods between west New Britain and other regions. In addition, this study identified a distinctive vessel form of double spouted pots of Lapita pottery that might originate from Island Southeast Asia, and demonstrates that after Lapita peoples had reached the Bismarcks, they maintained contact with homeland communities in Island Southeast Asia, and the double spouted pots were later introduced to the Bismarcks through interactions.

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  • Motherhood and Family Law

    Mackenzie, Fiona Amy (2016)

    Doctoral thesis
    University of Otago

    Throughout the broad sweep of history and related disciplines, including the law, can be found instruction with respect to the issue of motherhood. In one sense, it transcends culture; in another, it is a cultural construct. It is imbued with gender specificity and is profoundly important to children. This thesis explores motherhood’s relationship with family law and seeks to illustrate how, through uneasy tensions over time, it may have been compromised in modern child care law in New Zealand. It discusses whether parenting law should continue to adopt a gender neutral approach or whether, in considering a child’s welfare and best interests, there may be a case for greater recognition and restoration of gendered parenting relationships and perhaps, therefore, a repeal of s4(3) of the Care of Children Act 2004.

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  • Lapita Plants, People and Pigs

    Tromp, Monica (2016)

    Doctoral thesis
    University of Otago

    The Lapita cultural complex is associated with the Austronesian expansion out of Island Southeast Asia beginning approximately 3,500 BP. Sites associated with this archaeological culture have been found from the coast of New Guinea in Near Oceania and out past the Solomon Islands into Remote Oceania as far south as New Caledonia and as far east as Samoa by 2,700 BP. Major components of this culture include the commensal animals and horticultural plants that were transported with them as a portable subsistence economy during their voyaging. The commensal animal component of this package is reasonably well established, but the plant portion is less clear. This is primarily due to the scarcity of plant macro remains that have been found from archaeological sites and the lack of specificity of actual foods consumed in stable isotope analyses of archaeological human and animal bone. One direct way to explore the dietary plant component is to identify micro particles of plants (microfossils) that have been trapped within calcified plaque (dental calculus). The primary aim of this thesis is to examine the relationship between Lapita and immediately post-Lapita people and plants. The secondary aim is to examine whether human and commensal pig plant diets are similar and if it is possible to use pig diet as a proxy for human diet when human remains are not available for analysis. To address these aims, microfossils were extracted from human and pig dental calculus from four different sites: the SAC site on Watom Island, East New Britain Province, Papua New Guinea; Teouma on Efate Island, and Vao and Uripiv islands off the coast of northeast Malakula in Vanuatu. The samples were examined using a combination of light microscopy and scanning electron microscopy. All of the samples analysed date between Lapita (~3000 cal BP) and post-Lapita (~2500 cal BP) periods. These sites allow for a comparison of 1) an initial colonizing population (Teouma) and later populations (Watom, Uripiv and Vao), 2) Near Oceanic (Watom) and Remote Oceanic (Teouma, Uripiv and Vao) sites and 3) the wild versus cultivated plant components of their diets. The results show a much more diverse plant diet than has previously been shown. The importance of indigenous trees and shrubs to both Lapita and post-Lapita people analysed from all sites has been demonstrated in this study. Novel results include the first instance of banana seed phytoliths outside of the Bismarck Archipelago and an early introduction of Dioscorea esculenta to Vanuatu. The appearance of these non-indigenous plants at Teouma provides support for the concept of a “transported landscape”. However, the majority of identified plants were indigenous tree crops that suggest Lapita colonists were at least partly reliant on the forest resources that already existed on the islands they inhabited. This study represents the first direct plant evidence for Lapita and immediately post-Lapita diet of humans and pigs from this region.

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  • Improving Clustering Methods By Exploiting Richness Of Text Data

    Wahid, Abdul (2016)

    Doctoral thesis
    Victoria University of Wellington

    Clustering is an unsupervised machine learning technique, which involves discovering different clusters (groups) of similar objects in unlabeled data and is generally considered to be a NP hard problem. Clustering methods are widely used in a verity of disciplines for analyzing different types of data, and a small improvement in clustering method can cause a ripple effect in advancing research of multiple fields. Clustering any type of data is challenging and there are many open research questions. The clustering problem is exacerbated in the case of text data because of the additional challenges such as issues in capturing semantics of a document, handling rich features of text data and dealing with the well known problem of the curse of dimensionality. In this thesis, we investigate the limitations of existing text clustering methods and address these limitations by providing five new text clustering methods--Query Sense Clustering (QSC), Dirichlet Weighted K-means (DWKM), Multi-View Multi-Objective Evolutionary Algorithm (MMOEA), Multi-objective Document Clustering (MDC) and Multi-Objective Multi-View Ensemble Clustering (MOMVEC). These five new clustering methods showed that the use of rich features in text clustering methods could outperform the existing state-of-the-art text clustering methods. The first new text clustering method QSC exploits user queries (one of the rich features in text data) to generate better quality clusters and cluster labels. The second text clustering method DWKM uses probability based weighting scheme to formulate a semantically weighted distance measure to improve the clustering results. The third text clustering method MMOEA is based on a multi-objective evolutionary algorithm. MMOEA exploits rich features to generate a diverse set of candidate clustering solutions, and forms a better clustering solution using a cluster-oriented approach. The fourth and the fifth text clustering method MDC and MOMVEC address the limitations of MMOEA. MDC and MOMVEC differ in terms of the implementation of their multi-objective evolutionary approaches. All five methods are compared with existing state-of-the-art methods. The results of the comparisons show that the newly developed text clustering methods out-perform existing methods by achieving up to 16\% improvement for some comparisons. In general, almost all newly developed clustering algorithms showed statistically significant improvements over other existing methods. The key ideas of the thesis highlight that exploiting user queries improves Search Result Clustering(SRC); utilizing rich features in weighting schemes and distance measures improves soft subspace clustering; utilizing multiple views and a multi-objective cluster oriented method improves clustering ensemble methods; and better evolutionary operators and objective functions improve multi-objective evolutionary clustering ensemble methods. The new text clustering methods introduced in this thesis can be widely applied in various domains that involve analysis of text data. The contributions of this thesis which include five new text clustering methods, will not only help researchers in the data mining field but also to help a wide range of researchers in other fields.

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  • Assessing Learning, Breathing and Treatment of Respiratory Obstruction During Sleep in School Children: The ALBATROSS Study

    Maessen, Sarah Elizabeth (2016)

    Doctoral thesis
    University of Otago

    Introduction: Children with enlarged tonsils and/or adenoids are at risk for sleep disordered breathing (SDB), a common disorder in childhood characterised by snoring, choking, and pauses in breathing during sleep. SDB has been associated with a number of adverse effects on aspects of daytime functioning, including quality of life, behaviour, general cognitive functioning and memory. It has been documented that these difficulties can have a negative effect on school performance, but it is not known how children with SDB may differ from day to day in their school performance, or how their academic growth from week to week may be different from children without SDB. Furthermore, treatment of SDB by removing obstructive tonsillar and adenoid tissues can result in improvements in SDB symptoms, quality of life, and behaviour, but it is unclear whether this extends to school achievement. Previous research has used measures of academic performance such as parent and teacher report or standardised achievement tests. These kinds of measurements are not able to provide information about growth in academic achievement, and are not designed to be sensitive to treatment effects. The current research is a case series examining children on the waiting list for adenotonsillectomy (AT), a high risk group for SDB, using a multimethod-multi-informant approach to assessment. These children were assessed in domains where changes have previously been demonstrated after AT, i.e., SDB symptoms, quality of life and behaviour, as well as in academic performance, where results of previous research have been more equivocal. Methods previously used in SDB research to assess academic performance were used alongside alternative indicators of progress in literacy and numeracy. These measures were informed by evidence-based measurement approaches used to evaluate academic intervention, and were selected to probe skills specific to each child’s school year. This approach has previously demonstrated sensitivity to treatment effects in interventions for neurodevelopmental disorders. Methods: 20 case children aged 3-11 years were recruited from the waiting list for adenotonsillectomy at Dunedin Public Hospital. 19 of these children were matched to controls for age, sex, and school year, including academic performance where possible. 44% of participants were male, and 46% were preschool aged. All children were described in terms of their symptoms of SDB using parent ratings on the Pediatric Sleep Questionnaire, quality of life using the OSA-18 and Pediatric Quality of Life Inventory, behaviour using the SWAN rating scale and BASC-2 BESS , general cognition using the WPPSI-III and WISC-IV, and academic performance at matched time points both before surgery and at a follow up 7 months after surgery. In addition, an AHI was derived from home-based sleep studies conducted both before surgery and at a 3 month follow up. Academic performance was measured using parent and teacher judgements in relation to National Standards, performance on a standardised achievement test (WIAT-II Australian), and using the developmentally appropriate literacy and numeracy measures that were expected to be sensitive to changes across the study. The literacy and numeracy indicators were administered twice, one week apart, at each time point: twice before surgery (pre-‘surgery’), twice at the 3 month follow up (post-‘surgery’), and twice again at the 7 month follow up. These assessment points are similar to the timeline of previous SDB research. The current research takes both visual and statistical approaches to data analysis, allowing for examination of individual case-control pairs and within-subjects changes as well as group-level statistics. Results: At pre-‘surgery’, case children on average had more parent-reported SDB symptoms than matched controls (p = .001). This pattern was confirmed by AHI from overnight sleep studies indicating that the majority of case participants had clinically significant levels of SDB. As well as increased SDB symptoms, case children on average had poorer quality of life (range p = .001 - .032), behavioural and emotional functioning (p = .020), and memory (p = .001) than matched controls according to parent ratings. Teacher ratings did not suggest elevated levels of behavioural or emotional difficulties for either cases or controls and did not differ between groups, and mean general cognitive functioning scores were also similar between the groups. Typically used measures of academic performance, parent and teacher report and standardised achievement test scores, did not differ on average between case and control children, although case participants’ scores on the WIAT-II mathematics composite score were in the ‘low-average’ range compared to norms. Comparisons of literacy and numeracy indicators between the two pre-‘surgery’ sessions suggested that in general, case children appeared to have more consistent performance than controls from week-to-week, but less growth in these skills. When looking at mean performance on the tasks at pre-‘surgery’, several control children were outperforming their matched case participant, but there was a lot of individual variation in scores. After surgery, case children had improved parent ratings of SDB symptoms (p = .001), quality of life (range p = .001 - .023), behavioural and emotional functioning (p = .008), and memory (p = .014). With the exception of SDB symptoms and memory difficulties, which remained elevated for case children in comparison to matched controls, case and control children no longer differed statistically for mean scores in any other domain of daytime functioning. Teacher ratings of reading in relation to National Standards improved for case children (p = .011), but no other typically used measures of school performance changed notably following surgery. Improvements in scores on the literacy and numeracy indicators suggested different patterns of growth for different academic domains and age groups. For preschoolers, case children showed evidence of linear growth in an early literacy composite that was steeper than for control children on average (p = .008). However, improvement in early numeracy scores suggesting growth in these skills did not differ between case and control participants on average. Year 1 and 2 case participants showed considerable growth in a phoneme segmentation fluency task that was not observed for their matched controls, but there were no clear patterns for any other literacy or numeracy tasks. Children in Years 3 to 5 had improvements in literacy tasks that for some participants were greater than their matched controls, but did not appear to improve in numeracy. Year 6 and 7 students, in contrast, demonstrated evidence of growth in numeracy tasks, but most did not improve in literacy tasks. Conclusions: This research is consistent with previous studies reporting that children with SDB are at risk for poor academic performance or growth. The literacy and numeracy indicators used in the current research provided information about academic performance in these children beyond what could be ascertained from more conventionally used measures. This finding suggests that these more sensitive measures of academic growth have potential for evaluating effects of SDB treatment on academic performance in a larger group of children. The current study has clearly demonstrated that children who are undergoing surgery for removal of tonsils and adenoids in Dunedin are likely to have more symptoms of SDB and related negative effects on daytime functioning when compared to similar children in the community. It also provides preliminary evidence that treatment of SDB in early childhood may help to improve learning trajectories in literacy skills, supporting existing evidence for early identification and intervention for SDB. Many children are affected by health problems other than SDB or behavioural difficulties that have been associated with poorer school performance. The literacy and numeracy indicators used in the current research show promise for assessing the effects of surgical intervention for SDB, and therefore have the potential to explore the effects that treatment of other disorders that can affect school performance, such as otitis media (glue ear) or ADHD, could have on academic achievement.

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  • Informed preferences in forest-based land use planning in Indonesia : a methodological case study.

    Rahardja, Teguh (2005)

    Doctoral thesis
    University of Canterbury Library

    Indonesia is large and rich in natural resources. Its forest extends over 60 per cent of the country's land and contains many other natural resources. There are many stakeholders, often with conflicting interests. The demands placed on the forest have resulted in declining quantity and quality of the forest lands. People have recognised the need for reviewing and improving the forest-based land use plan, and, in so doing, promoting the participatory approach rather than the traditionally centralistic one. This has been attempted, but there were difficulties in the participatory evaluation of land use options' impacts. Therefore, this study aims to develop a method to help forestry-based land use planning take into account stakeholders' preferences after considering land use scenario consequences. Based on the situation in Indonesia and existing options, this study adopted the mixed rational-participatory approach. The rational side was attempted by FOLPI simulation of land use scenarios. An interview survey of opinions suggested eight scenarios of varying emphases on the economic, ecological and social aspects, which were simulated in FOLPI with area and resource data of each land use. The results were graphs of land use changes and their economic, ecological and social impacts. The participatory aspect was promoted by Q methodology applications. Q was used to analyse respondents' sorts of a set of statements about different aspects of land use planning, and revealed the typology and preferences of stakeholders with regard to land use planning. Using verbal statements in such exercises discovered the typology and normative preferences, while using the FOLPI application graphs as the statements disclosed the positive preferences. In tandem, they provide useful information as inputs to stakeholder deliberations towards a new, rational, and acceptable land use scenario. This study, therefore, recommends a method to help forest-based land use planning stakeholders. The method includes FOLPI simulation of the broad-scoped land use scenarios, and Q applications both the conventional verbal way and the innovative graphical way.

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  • Advanced surface texturing for silicon solar cells

    Ganesan, Kumaravelu (2005)

    Doctoral thesis
    University of Canterbury Library

    The multi-crystalline silicon (me-Si) solar cell is considered to be one of the most promising cells capable of achieving high efficiency at low cost and high reliability. Improving solar cells efficiency using low cost materials requires careful design considerations aiming to minimise the optical and electrical losses. In this work plasma texturing was employed to reduce optical reflections from silicon surfaces well below 1%. Plasma texturing is used to form light trapping structures suitable for silicon solar cells. Several plasma texturing methods are investigated and associated defects are analysed. Masked as well as mask-less texturing techniques are investigated. Conventional parallel plate Reactive Ion Elching (RIE), Inductively Coupled Plasma (ICP) and Electron Cyclotron Resonance (ECR) plasma system are used to compare the plasma induced defects in silicon. The influence of various plasma etch parameters on plasma induced defect is investigated. A correlation between the minority carriers lifetime and surface area increased by texturing is established. Effective lifetime measurements using Quasi Steady State Photo Conductive (QSSPC) technique is mainly used to estimate the plasma induced defect in textured silicon substrates. Sinton lifetime tester is used to measure the effective lifetime of the substrates. The implied open circuit voltage is calculated from the lifetime data for textured substrates. In this work low temperature photoluminescence spectroscopy is also used to analyse the defect caused by plasma on me-Si substrates. Photoluminescence (PL) data is obtained using the 514.5 nm line of an Ar⁺ laser as an excitation source. The luminescence is dispersed with SPEX 1700 spectrometer with a liquid nitrogen cooled Germanium detector. Reflectance measurements are performed on textured surfaces usmg a purpose built integrating sphere attachment of a high accuracy spectrophotometer. Modelling is also performed using PV-optics software to compare the experimental and theoretical results. Finally, silicon solar cells are fabricated with measured efficiency around 18% . The efficiency is estimated from the I-V characteristics data obtained using a calibrated halogen lamp and a HP semiconductor parameter analyser. Spin-on-dopant source as well as solid diffusion source is used to form the ewitter junction of the solar cells fabricated on p-type silicon wafers. Multicrystalline silicon, CZ- silicon and FZ silicon wafers are used to fabricate solar cells in this thesis. The effect of single and double layer antireflection coatings on diffused reflections is also investigated.

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  • Wavefront estimation in astronomical imaging.

    Irwan, Roy (1999)

    Doctoral thesis
    University of Canterbury Library

    The challenge in building astronomical telescopes is to obtain the clearest possible image of a distant star, which should appear as a single point. Extended objects, such as galaxies and planets can be regarded as collections of points. However, turbulence in the atmosphere degrades any optical signal that passes through it. The optical effects of the atmospheric turbulence arise from random inhomogeneities in the temperature distribution of the atmosphere. As a consequence of these temperature inhomogeneities, the index of refraction distribution of the atmosphere is random. Plane waves striking the atmosphere from space objects acquire an aberration as they propagate through the atmosphere. The plane wave's surface of constant phase is no longer planar when intercepted by a,n a.stronornica.l telescope. The prnctica.l consequence of a.tmospheric turbulence is that resolution is generally limited by turbulence rather than by optical design and quality of a telescope. There are a number of approaches to solving this problem, ranging from an orbiting telescope (the Hubble Space Telescope), adaptive optics, and post detection processing. The latter approaches have applications to less expensive ground based telescopes and have been the subject of many years of research. Adaptive optics is a general term for optical components whose characteristics can be modified in real time so as to alter the phase of an incident optical wavefront. An adaptive optics system can be used to correct for atmospheric induced distortions. Before any corrections can be applied, however, some measurement must be made of the phase distortions. It is the aim of this study to estimate the degradation of the wavefronts phase. Two approaches to do so are presented. Firstly, through wavefront sensors, which many adaptive optics systems have been devised from. Among them the Shack-Hartmann sensor is the most commonly used. The sensor requires a subdivision of the receiving pupil by means of sub-apertures, wherein the lowestorder deformation of the wavefront phase is estimated. This linearizes the problem of phase retrieval to solving a linear system of equations. A new analysis is presented which differs from previously published work in the estimation of the noise inherent in the centroid calculation used in this sensor. This analysis is supported by computer simulations. Secondly, the nonlinear approach of phase retrieval is discussed. The problem becomes how to relate the phase and magnitude of the Fourier transform. It is thus necessary to estimate the phase distortion in the instrument solely from measurements made at the image plane of the telescope. The process of phase retrieval is then divided into two distinct steps. The expression for the covariance of the phase distortion using a Kolmogorov model for the turbulence is derived first. This covariance is then employed as part of a formal Bayesian estimate of the phase distortion. It is also shown that phase retrieval can be employed as a robust technique for estimating the wavefront distortion using a lenslet array. The results obtained compare favorably with the alternative approach of phase diversity. Furthermore, the introduction of prior information, in the form of statistical information of the distortion, is shown to considerably enhance the success of the phase retrieval especially for very low light levels. A comparative evaluation shows the superiority of phase retrieval to Shack-Hartmann sensing, only if the local maxima are overcome. The principal drawback of phase retrieval is the relatively long computing time required to find the solution when general-purposed computer is used.

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