5,261 results for 2015

  • A Novel Biodegradable Fe-35wt.%Mn Alloy Produced via Powder Metallurgy

    Zhang, Qian (2015)

    Doctoral thesis
    The University of Auckland Library

    This doctoral project permitted to design, develop and study a degradable metallic biomaterial. Between 2011 and 2015, magnesium alloys and commercially pure iron were evaluated for their possibility for the use in biomedical areas. Their mechanical properties and degradation behaviors were not clinically well suited. Hermawan et al. investigated a series of Fe-Mn alloys via a powder metallurgical (PM) route followed by cold rolling and re-sintering cycles and found that manganese content of 35 wt% alloy was nonmagnetic and cell compatible. However, as a fully dense alloy, the degradation rate was still not satisfactory. In this doctoral project, the Fe-35wt.%Mn alloys were produced via several PM routes. This research employed three different starting powders, which were blended elemental (BE), mechanically milled (MMed) and BE powder with porogen. We aimed to develop a less dense alloy that has a higher degradation rate, suitable mechanical properties and good cell compatibility. The Fe-35Mn alloys were firstly fabricated by a simple blend-press-sinter method. Sintering temperatures and holding times were varied to investigate their influences on the microstructure evolution, densification, corrosion behavior as well as mechanical properties. The increase of sintering temperature and holding time led to the decrease of porosity level of the sintered compacts. Among these parameters, a sintering temperature of 1200??? and a holding time of 4 hours proved to be able to produce samples with a good densification level. The change of sintering temperature and time did not affect the final phase where non-ferromagnetic austenitic ?? and martensitic ?? were the main phase. A satisfactory degradation rate of 1.5 to 4 mmpy was obtained; but the mechanical strength was low. In order to enhance the mechanical properties, a mechanical milling (MMing) process was employed to obtain finer starting powder particles. The MMing parameters were investigated and ball-to-powder (B-P) ratio of 5:1 and milling time of 6 hours were identified to be able to produce the required powder. After milling, various pressing pressures using a steel die press were employed, followed by cold isostatic pressing (CIPing) at 200 MPa. Higher compaction pressure resulted in lower porosity level and CIPing further enhanced the densification. When compared with the BE powder, reducing the powder particle size via MMing had led to a decrease in porosity to 7 ~ 12%. Hence, a significant improvement of mechanical properties was then achieved. Porogen ammonium bicarbonate (NH4HCO3) particles were added to fabricate porous Fe-35Mn alloy foam which had varying degrees of porosity level. By the addition of 10 and 20 volumetric percent of NH4HCO3, the degradation rates of the Fe-35Mn samples with the introduction of the NH4HCO3 porogen were significantly accelerated when compared with the samples without NH4HCO3 addition. The electrochemical corrosion rates were ranging from ca. 2 to 8 mmpy in both 5% NaCl and SBF solutions. The proposed degradation mechanisms were uniform corrosion in addition to crevice corrosion. Iron ion release during a one-month???s dynamic corrosion was slightly higher than that of manganese. However the mechanical properties of these Fe-35Mn foams posed a limitation for the development of Fe-35Mn foams in the load-bearing applications. The stress corrosion cracking (SCC) investigation in a physiological environment followed. A slow strain rate test (SSRT) method was used in order to achieve a better understanding with regard to the stress corrosion behavior. The SCC susceptibility was sensitive to the strain rate and the testing environment. A slower strain rate and a more aggressive environment resulted in a higher SCC susceptibility. The higher density level of the sintered samples led to a reduction of SCC susceptibility. Intergranular fracture was observed on the sample surface of all tested specimens. SCC cracking was initiated from crevices and pores in both BE and MMed Fe-35Mn alloy samples. The cytocompatibility of Fe-35Mn alloys were then investigated using an indirect cell-material interaction by culturing L929 cell line in Fe and Mn ion-rich elution containing up to 1.29 and 1.12 ppm of released Fe and Mn ions. Results showed L929 mammalian cells proliferated and grew healthily in all testing extractions. It was suggested that Fe-35Mn alloys were biocompatible since no significant difference was found in the cell viability response to the material elutes. It has to be pointed out that the simple blend-press-sinter method was able to produce a Fe-35Mn alloy that met degradation requirement. MMing could increase the samples??? mechanical strength. However the strength level is still insufficient for load-bearing applications. A further investigation of optimizing the PM parameters is needed to increase mechanical strength while maintaining sufficiently fast degradation.

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  • High functioning autism and common coexisting conditions: An EEG investigation

    Bullot, AK (2015)

    Doctoral thesis
    The University of Auckland Library

    Autism spectrum disorder is a lifelong neurodevelopmental condition for which there is no known cure. The rate of psychiatric comorbidity (and comorbidity with other neurodevelopmental disorders) in autism is extremely high, which raises questions about the nature of the co-occurring symptoms. It is unclear whether these additional conditions are true comorbid conditions, or simply behaviour that is better conceptualised through the ASD diagnosis. The overall aim of the current thesis is to investigate the shared behavioural and neural basis of coexisting ADHD and anxiety in ASD. The studies in the current thesis consisted of an investigation of behavioural characteristics using profiling techniques (Total n = 83 (ADHD = 23; anxiety = 12; ASD = 25; controls = 23)), in addition to four experimental studies conducted during concurrent EEG recording. These tasks were: emotion processing (Total n = 74 (ADHD = 22; anxiety = 12; ASD = 20; control = 20)); lexical decision (Total n = 83 (ADHD = 21; anxiety = 12; ASD = 20; control = 20)); inhibitory control (Total n = 57 (ADHD = 16; anxiety = 9; ASD = 15; control = 17)) and a resting state recording (Total n = 46 (ADHD = 11; anxiety = 10; ASD = 13; control = 12)). The diagnostic categories listed above include those with a comorbid condition, the groups are split further with respect to comorbid condition (e.g., ASD pure, ASD and comorbid ADHD) in each study. Together, these experiments covered a spectrum of core difficulties evident in ASD: difficulties with social interactions; language; repetitive behaviour (inhibitory control) and aberrant brain growth. By examining difficulties with they occur alone in ASD versus together with ADHD or anxiety, we are able to build a profile of singular and co-occurring ASD. In the behavioural profiling study, using the wider diagnostic categories (e.g., ASD, ADHD and anxiety), results demonstrate that each group was able to be distinguished from one another, and from neurotypical controls, using the profiling measures. In individuals who present with both ASD and anxiety together, the symptoms of ASD are not significantly higher, but symptoms of anxiety do increase compared to those with ASD alone. This suggests that anxiety is a separate condition when it occurs together with ASD. When ASD and ADHD occur together, there were significantly higher ASD symptoms than in the ASD only group and significantly lower ADHD symptoms than the ADHD alone group (but not the ASD only group). This suggests that there might be some degree of symptom overlap when ASD and ADHD present as a comorbid condition. In the emotion processing task, there were no group differences in the latency or amplitude of the N170. There were, however, differences in the amplitude of the P250. Those with ASD and ADHD showed a differential profile in response to sad and neutral stimuli on the P250 from one another. Those with ASD had larger amplitudes toward mouth stimuli than eye stimuli, and those with ADHD had larger amplitudes toward eye stimuli than toward mouth stimuli. In addition, there was larger N170 amplitudes in the ASD pure group versus those with ASD and anxiety or ADHD. This suggests an additive effect. In the lexical decision task, overall, the results indicated larger P100 amplitudes in the right versus the left hemisphere (most strongly shown in control participants). When the ASD and ADHD present as a comorbid condition, the mean P100 latency for the comorbid group lay between the two means for the ASD and ADHD pure groups. This suggests an additive effect. In the inhibitory control study, the group level analysis did not show any differences between the experimental groups on the latency or amplitude of the N2 or P3 components. Upon closer inspection using regression analyses, smaller N2 and P3 amplitudes were associated with more severe symptoms of ADHD. Therefore, it is possible that inhibitory control deficits are associated with ADHD but not ASD or anxiety. In the resting state study, the results demonstrate patterns of decreased coherence in those with ASD, and patterns of increased coherence in ADHD and anxiety compared to neurotypical controls. The patterns of coherence established in the ASD pure group are no longer evident when comorbid conditions are included in the analyses. Thus, this suggests that the conditions are additive. Taken together, the studies in this thesis demonstrate that when ASD presents as a comorbid condition, ERPs adopt unique characteristics of each condition in its pure form. We argue that this is evidence for an additive effect which suggests that the conditions are indeed separate, rather than a misinterpretation (or increased severity) of ASD symptoms. This information is important to researchers when screening for comorbid conditions in ASD research, as underlying brain activity appears to be altered in each condition. This may significantly influence research findings. In addition, the results of the current study will also help to inform medical practitioners when administering a diagnosis and deciding on a plan to treat specific difficulties associated with comorbid ASD.

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  • Haemodynamic Assessment of Coronary Flow with CFD and Phase-Contrast MRI

    Beier, Susann (2015)

    Doctoral thesis
    The University of Auckland Library

    Coronary artery atherosclerosis is a major cause of morbidity and mortality worldwide. Some anatomical characteristics of coronaries may increase the likelihood of disease development, and stenting, a common treatment, has a high probability of restenosis and in-stent thrombosis. Coronary flow patterns, determined by vessel geometry and stent design and deployment, are thought to be related to adverse clinical outcomes. This thesis represents a comprehensive assessment of the relationships between flow and major coronary artery shape, and stent design and deployment. It further demonstrates the feasibility of assessing dynamically scaled coronary phantom flow with phase-contrast magnetic resonance imaging (PC-MRI). A range of idealised and patient-specific coronary artery geometries, with and without stents, were generated based on a statistical shape database from computed tomography (CT) angiograms, and micro-CT scanned benchtop deployed stents, using a computer aided drawing program. Transient flow was simulated using computational fluid dynamics (CFD). The geometries were also up-scaled, 3D printed, and incorporated into a dynamically scaled blood-analogue flow circuit for velocity acquisition with PC-MRI. The CFD results revealed little flow effect for bifurcation angle when varied in non-stented and stented idealised and patient-specific bifurcations. Flow was also computed in four patient geometries with wide shape variation, where a statistical shear stress analysis suggested that the vessel tortuosity may influence the effect of bifurcation angle. Similarly complex flow alterations were observed when systematically analysing the flow effects of major stent design features. The haemodynamic interrelations provided insights for the development of design guidelines for stent manufacture. Computational findings were validated by means of a new approach using dynamically scaled phantom flow and PC-MRI acquisition for non-invasive imaging with higher effective resolution (7-fold up-scaled geometries). The co-registered flow fields yielded good agreement (R2>0.8, magnitude error <8%) after using the PC-MRI measured inlet flow to inform the computational boundary conditions. A complementary approach of CFD and dynamically scaled PC-MRI can deliver further insights into the important haemodynamic effects of vessel shape and stent design and deployment. The results represent a potential clinical assessment tool, new considerations for stent design guidelines and deployment strategies, and a novel approach for coronary flow assessment for patient-profiling and pre-surgical planning.

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  • Construing consumer resistance: comparing Tongan and European female non-smokers in New Zealand

    Fifita, Ilaisaane (2015)

    Doctoral thesis
    The University of Auckland Library

    Smoking remains the largest cause of preventable morbidity and mortality worldwide and in 2011 New Zealand committed to the goal of being smoke-free by 2025. Despite decades of comprehensive tobacco control efforts and an overall reduction in tobacco use, M??ori and Pacific peoples have substantially higher smoking prevalences than the general New Zealand population. There is also an increased risk of lung and breast cancer incidence in M??ori and Pacific women. Prior research suggests that females and people from more collectivist cultures are more susceptible to interpersonal influence and are therefore more vulnerable to peer pressure to try smoking. Once smoking is started, its addictive nature makes it extremely difficult to give up. The more people in a group who smoke, the more likely it is that others in their group will take up smoking, creating a vicious cycle. To move the field forward and achieve the smoke-free goal by 2025, it is important to understand how people can resist smoking even in the face of interpersonal influence. Responses to peer pressure may be influenced by a person???s cultural values and norms. Selfconstrual, the way one construes self in relation to others, is a useful lens for understanding cultural differences in smoking resistance. However, much of the relevant prior empirical research on smoking prevention/cessation and self-construal is based on people from Western cultures, potentially limiting the applicability of these findings to people from non-Western cultures. Consequently, the study reported in this thesis sought to shed light on how selfconstrual influences smoking resistance among New Zealand Tongan (Tongan) females, using New Zealand European (NZE) females as a comparison group. In-depth interviews conducted with 29 (14 Tongan and 15 NZE) females who self-identified as non-smokers were open, axial and selectively coded before being interpreted against the context provided by the relevant literature. The findings revealed that non-smokers were initially motivated to resist smoking initiation because they wished to avoid the negative consequences of smoking and/or to gain the positive consequences of not smoking. The findings further revealed that creating and maintaining a smoking-resistant identity was central to successful, long-term smoking resistance in both cultural groups interviewed. Specific values, traits and coping strategies were found to help sustain smoking-resistant identities. Finally, the findings revealed the importance of self-construal in unpacking how both Tongan and NZE women resist smoking. Although independent self-construals were central to NZE women???s resistance to smoking, both independent and interdependent self-construals were important in Tongan women???s smoking resistance. The thesis concludes with a discussion of the theoretical, methodological and substantive contributions.

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  • Zinc-Magnesium and Zinc-Aluminium- Magnesium Coatings Produced by Magnetron Sputtering and Melt Dipping

    Yao, Caizhen (2015)

    Doctoral thesis
    The University of Auckland Library

    Zn coating is the most economic and widely used sacrificial coating to protect steels against corrosion. Since the corrosion resistance of pure Zn coating is not satisfactory under alkaline or high humidity environments, over the past few decades, demands for better corrosion resistance and mechanical properties arising from various industries and sectors have driven the research and study on alternative coatings of pure zinc coating. The most successful substitutions are Zn-Al alloy coatings, e.g. zincalume (55% Al-44% Zn-1% Si) and galfan (5% Al) coatings. These coatings combine the sacrificial protection of zinc and a long lasting physical barrier of alumina together, thus corrode 5-10 times slower than pure Zn coating. Recently, Zn-Mg and Zn-Al-Mg coatings have been developed from the traditional Zn and Zn-Al coatings by the addition of small amount of Mg. A great attention has been attracted due to their excellent properties. Evidence suggests that up to a 10-fold drop in weight loss has been found in Zn-Mg coating in comparison with pure Zn coating. The performance of Zn-Al-Mg coating in salt spray test is better than that of Zn coating by 10-20 times and Zn- Al coating by 2-5 times. Furthermore, Zn-Al-Mg coating is found to have self-healing capability. Various coating methods, including hot dipping and physical vapour deposition (PVD), have been employed in past studies, and each method results in its unique microstructure and properties in the coating. Those coatings can be used in perforated plates in civil construction, automobile bodies and parts, green house structures in agriculture and switch cabinets in electric power and telecommunication applications. The improvements of corrosion resistance properties from addition of Mg in Zn-(Al)-Mg coatings have been evidenced by researchers. However, detailed information on the corrosion mechanism of Zn-(Al)-Mg coatings is still lack in open literatures, and a number of unclear factors need to be investigated. For example, the effect of Mg content on the microstructure of Zn-(Al)-Mg coating; how does the microstructure interrupt the corrosion process of Zn-(Al)-Mg coating; is there an economic way for the mass production of Zn-(Al)- Mg coating to substitute the traditional Zn coating, and the environment that Zn-(Al)-Mg coating can be used. What???s more, as a novel technology, electrochemical method is seldom used in the study on corrosion properties of Zn-(Al)-Mg coating. This research aims to study the processing methods, microstructure and properties of Zn- (Al)-Mg alloys and coatings with varying Mg contents, to investigate the mechanisms of microstructure formation and corrosion behaviour. The ultimate aim is to apply this new type of coating into industrial practice. The processing methods adopted in this research are hot dipping, electroplating and magnetron sputtering. Alloys and coatings are characterized and tested by optical microscopy (OM), environmental scanning electron microscopy (ESEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), microhardness test and electrochemical tests e.g. Open circuit potential (OCP)-time curve, potentio-dynamic polarization curve, electrochemical impedance spectroscopy (EIS) have been used to investigate the morphologies, chemical compositions, mechanical and corrosion properties of coatings. Salt water immersion test (SWI) and neutral salt spray test (NSS) was performed to further investigate the corrosion properties and mechanisms of coating specimens. The main findings from this study include: (1) The microhardness of Zn-(Al)-Mg alloys increased with increasing Mg content, probably due to the grain refinement strengthening effect and the formation of more intermetallic phase at grain boundary areas. Potentio???dynamic polarization curves indicated that the Ecorr of Zn???3 wt.% Mg alloy is more positive than that of Zn, with a low icorr of ~34% of Zn, probably due to its nanostructure. The nano???structure of Zn + Mg2Zn11 eutectic in Zn???3 wt.% Mg alloy may contribute to a general precipitation of Mg???modified simonkolleite and retard localized corrosion, contributing to the excellent corrosion resistance of Zn???3 wt.% Mg alloy. Zn-5 wt.% Al-2 wt.% Mg alloy contains a large amount of Mg2Zn11, and it has the highest impedance 5.11??103 ohm according to EIS results and the lowest icorr 1.03??10???3 A/cm2 according to the polarization curves among tested Zn-Al-Mg alloys. We assume that the improved corrosion property may relate to the formation of Mg2Zn11 intermetallic. (2) The Polarization curves showed that corrosion resistance of Zn coating was enhanced significantly by the magnetron sputtered Zn-Mg layer. Salt water immersion test in 3.5 wt.% NaCl solution also showed corrosion property improvement. The corrosion products on magnetron sputtered Zn-Mg coating mainly contain Mg modified simonkolleite and magnesium hydroxyl carbonate. The much improved corrosion resistance of Zn-Mg coating can be attributed to the formation of the uniform layer of Mg modified Zn5(OH)8Cl2H2O compound. During the corrosion process, less noble Mg reacts preferentially and a layer of magnesium hydroxyl carbonate forms on the coating surface, which is electrochemically inert. The magnesium hydroxyl carbonate has the effect to neutralize the OH- associated with Zn5(OH)8Cl2H2O formation, resulting in the precipitation of Zn5(OH)8Cl2H2O. This uniform Zn5(OH)8Cl2H2O layer formed on coating surface further reduces the corrosion rate of Zn-Mg coating. (3) For hot dipped Zn-Mg coating, with the increasing of Mg content, a significant improvement in the microhardness was observed as a result of grain refinement strengthening effect and the formation of intermetallic. Based on the results of XRD and EDS analyses, it was concluded that laminar eutectic MgZn2 and Zn formed at Zn grain boundary areas during the solidification of the coating. Electrochemical test indicated that the current density of Zn???3 wt.% Mg coating was appreciably lower than that of Zn coating, suggesting that Zn???3 wt.% Mg coating possessed improved corrosion resistance. This result was further proved in salt water immersion test. The formation of flocculent type of simonkolleite may be a reason for its improved corrosion resistance. (4) For hot dipped Zn-Al-Mg coating, optical microscope images showed that with the increasing Mg content, Zn grain size decreased and eutectic areas at Zn grain boundaries increased. Zn-5 wt.% Al-1.5 wt.% Mg coating has two continuous layers. Mg is prone to exist in the surface layer while Al is prone to exist in the inner layer. The inner layer is composed of Al5Fe2Zn0.4 intermetallic and the outer layer is composed of Zn grains surrounded by Zn and Mg2Zn11 eutectic. This is a well combination of Zn, Al and Mg structure: the inner intermetallic layer containing Al increased the microhardness and adhesive properties of the coating and the outer layer containing Mg contributed to the corrosion resistance of the coating. Zn-5 wt.% Al-1.5 wt.% Mg coating showd the best corrosion resistance among tested Zn-Al-Mg coatings. The outstanding corrosion resistance property of Zn-5 wt.% Al-1.5 wt.% Mg coating is due to the formation of flocculent type of simonkolleite. The structure of simonkolleite prolongs the micro-path and impedes the movement of O2 and H2O, ultimately retards the overall corrosion process of Zn-5 wt.% Al- 1.5 wt.% Mg coating. (5) For Zn-Al-Mg-Cu coating, three different compositions (in wt.%) of dipping bath were prepared: Zn???0.1Cu (G), Zn???5Al???0.1Cu (ZA) and Zn???5Al???1Mg???0.1Cu (ZAM). Results showed that ZAM coating consists of five different phases: hcp Zn phase, base centered Al5Fe2Zn0.4 phase, laves phase MgZn2, cubic lattice Mg2Zn11 and Zn-Fe intermetallic compound. The microhardness of ZAM coating was improved to 178 HV comparing with 43 HV of G coating and 89 HV of ZA coating. The improved microhardness of ZAM coating is due to the strengthening effect of grain boundary at which intermetallic compounds of Al5Fe2Zn0.4, MgZn2 and Mg2Zn11 precipitated. ZAM coating has the best corrosion resistance among three types of coatings as evidenced by electrochemical test and salt spry test. The protective nature of ZAM coating may be attributed to the initial corrosion of Mg-rich phases. The corrosion products of Zn, Al and Mg agglomerate on the cathodic area, which act as inhibitors, blocking the corrosion paths (the micro paths for the diffusion of O2 and H2O) along the grain boundaries of Zn crystals, and increasing the impedance of coating surface, Thus, the overall corrosion process of ZAM coating is retarded. Future works for this research are also suggested in the end of thesis.

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  • An Improved Clinical and Pathophysiologic Characterisation of Post-Operative Ileus

    Vather, Ryash (2015)

    Doctoral thesis
    The University of Auckland Library

    INTRODUCTION Post-operative ileus is a major cause of morbidity globally. The objectives of this body of work are to classify and define ileus, evaluate the efficacy of Gastrografin in shortening its duration, predict the occurrence of prolonged ileus, and describe changes in peri-operative and post-surgical intestinal motility. METHODS A systematic literature review and online global survey were conducted to clarify terminology and provide concise, clinically quantifiable definitions for ileus. A retrospective cohort study, narrative review, and laboratory analysis were used to inform design and execution of a double-blinded, placebo-controlled, randomised trial investigating the therapeutic value of Gastrografin in shortening duration of prolonged ileus following elective colorectal surgery. Risk factors predictive of prolonged ileus following colorectal surgery were identified by a prospective cohort study. In vivo high resolution manometry was utilised to assess changes in intestinal motility peri-operatively and post-surgically. RESULTS Three classes of ileus can be identified and defined ??? post-operative ileus, prolonged post-operative ileus, and recurrent post-operative ileus. In an episode of prolonged ileus, orally-administered Gastrografin accelerates resolution of lower gastrointestinal symptoms (abdominal distension; absence of flatus and stool) but does not affect upper gastrointestinal symptoms (nausea and vomiting; intolerance of an oral diet). Independent predictors for prolonged ileus include male gender, decreasing pre-operative albumin, open/converted technique, increasing wound size, operative difficulty and bowel handling, total intravenous crystalloid, red cell transfusion, and day of first mobilisation. Ileus is underpinned by cyclic motor activity which occupies the majority of the immediate postoperative period; by contrast, short and long single motor patterns appear infrequently and sporadically. Those who have previously undergone segmental colorectal resection (and preserved normal bowel function) exhibit a normal colonic meal response with evidence of coordinated trans-anastomotic motor activity. CONCLUSIONS Three classes of ileus can be broadly identified and defined; Gastrografin is not clinically useful in shortening an episode of prolonged ileus; predictive scoring systems may identify individuals at risk of developing prolonged ileus; ileus is characterised by ubiquitous cyclic motor activity of likely myogenic origin; and normal motility is eventually restored in patients who have undergone segmental colorectal resection.

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  • The Tracking & Analysis of Cell Movement with Cell-Derived Active Contours & Generative Graphical Models

    Nejati Javaremi, Alireza (2015)

    Doctoral thesis
    The University of Auckland Library

    There has been a continuous effort (Li et al., 2009; Al-Kofahi and Lassoued, 2010; Al-Kofahi et al., 2011; Amb??hl et al., 2012; Meijering, 2012; Ma??ka et al., 2014) to provide tools for large-scale automated analysis of live cell morphology in vitro, as this very important for studying biological development and disease. In this thesis, we outline a set of theoretical and practical tools that we have developed for this purpose. In chapters 1-5 we present a new cell-derived active contour (CDAC) method for cell tracking that achieves higher tracking accuracy using knowledge about cell movements. This knowledge consists of the way cells move by adhering to the substrate and propelling their cell membranes in the direction normal to the edge. This allows use of fast optimal search methods. Our method is designed for phase contrast microscopy, which allows access to a wider variety of experimental data. It can operate under conditions of low illumination. This is important for live-cell imaging as high illumination can damage cells. Additionally, our method demonstrates a higher robustness to noise than many previous methods. We then develop a statistical framework for cell shape analysis. Due to the large dimensionality of the space of cell shapes, we first use a neural network model to extract a small set of relevant features. This allows efficient learning and this makes our method distinct from previous methods (such as kernel density estimation). We then develop a rotation-invariant framework - a property that has not been incorporated in previous cell shape model studies and is a limitation of other models - to construct a hierarchical Bayesian generative model to learn the distribution of cell shapes. We show that this new property allows, for the first time, deriving features such as elongation or cell asymmetry directly from the data without any prior assumptions. In this work we maintain a close relationship between experiment and theory. The problem of calculation of cell movement indices from experiment is studied and related to theoretical models. We also use theoretical models to validate our morphology analysis framework, showing good statistical agreement with natural cells.

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  • The Case for Subsidiarity as a Constitutional Principle in New Zealand

    Gussen, Benjamen (2015)

    Doctoral thesis
    The University of Auckland Library

    This doctoral thesis uses historical analysis, constitutional economics, and complexity theory to furnish positive and normative arguments for subsidiarity as a constitutional principle in New Zealand. The principle of subsidiarity is the hypostasis of the Treaty of Waitangi, both in its English and M??ori texts. It is also evident in the thinking behind the New Zealand Constitution Acts of 1846 and 1852. This constitutional tradition has been occulted since the abolition of the New Zealand provincial system in 1876. Constitutional economics suggests an optimal limit to jurisdictional footprints (territories). This entails preference for political orders where sovereignty is shared between different cities rather states where capital cities dominate. The resuscitation of subsidiarity as a foundational element of our constitution holds the key to economic prosperity in a globalising world. Moreover, insights from complexity theory suggest that sustainability is a response to the ???problem of scale???. It is a fitness trait that prevents highly complex systems from collapsing. The nation state is a highly complex system within which cities function as ???attractors???. The collapse of such systems would ensue if there were strong coupling between attractors. Such coupling obtains under legal monism. Only subsidiarity can make this eventuality improbable. Understanding the ???emergent properties??? of sustainability and the ???selforganizing??? properties of subsidiarity entails a shift in policy emphasis towards the latter. The thesis recommends changes to the Constitution Act 1986 to reinstitute subsidiarity as a constitutional principle. New Zealand cities, in particular the Auckland supercity, would benefit from wider local autonomy under this vision. Nevertheless, constitutional change will have to start with public opinion, especially in relation to subsidiarity and its role in shaping the relationship between cities and the central government.

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  • Disgust in colorectal cancer contexts: Does it cause avoidance and could mindfulness help?

    Reynolds, Lisa (2015)

    Doctoral thesis
    The University of Auckland Library

    Disgust???s evolved function is to minimise health threats through a process of rejection, avoidance, and withdrawal. Despite its seemingly obvious relevance, however, research investigating disgust in physical health settings remains scant. By exploring the emotion of disgust in the context of colorectal cancer, the current work sought to address this research deficit, and in doing so, add to the emerging literature examining the emotional bases of avoidance in health. The colorectal cancer trajectory presents numerous established disgust elicitors (faeces, surgical wounds, anal investigations, etc.), and avoidance can have serious physical and psychological consequences. Thus, the aims of this work were to establish: (1) whether disgust predicts and/or causes avoidance in colorectal cancer contexts, and if so, (2) consider whether mindfulness may help to ameliorate this effect? Following a systematic review of literature pertaining to colorectal cancer and disgust, a series of correlational and experimental studies in clinical and non-clinical populations were conducted. The first of these empirical works???Study 1, a prospective, correlational design with anal incontinence patients???found that greater disgust sensitivity predicted poorer psychological and environmental well-being, and moderated the link between symptom severity and outcome. In Study 2a, trait disgust predicted, and experimentally-induced disgust caused, greater immediate avoidance behaviours related to colorectal cancer. In addition, trait disgust increased the influence of state disgust on decisions regarding anticipated future avoidance. With the relationship between disgust and avoidance established, the focus of this work then turns to consider whether mindfulness might ameliorate disgust???s effects. Data from the prior study was revisited in Study 2b, and contrary to expectations, analyses showed that greater trait mindfulness exaggerated avoidance behaviours rather than diminishing them. Similarly, Study 3???an experimental study in which both disgust and mindfulness were experimentally induced???found that state disgust caused social avoidance in relation to bowel health scenarios and, again, state mindfulness exaggerated the effect. Finally, Study 4, a randomised controlled trial with first time chemotherapy patients, found that a brief mindfulness intervention led to detrimental effects???greater distress and increased social avoidance???in comparison to relaxation training. Taken together, these studies are the first to clearly demonstrate that (a) disgust both predicts and causes avoidance in contexts related to colorectal cancer, and (b) that mindfulness does not ameliorate disgust???s effects, at least in these contexts. This thesis thus highlights the importance of considering the emotion of disgust in both colorectal cancer and in physical health settings more broadly, and has important clinical implications. Through better understanding of a key affective mechanism of avoidance (i.e., the disgust response), these findings have potential to inform interventions designed to reduce deleterious avoidance. This work ends on a note of caution, suggesting that mindfulness-based interventions may not be optimally suited to some physical health populations, and suggests alternative potential avenues for future research and clinical intervention.

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  • Structural and functional studies on pantetheinylation: An essential post-translational modification in two pathogenic bacteria

    Jung, J (2015)

    Doctoral thesis
    The University of Auckland Library

    Pantetheinylation is a form of post-translational modification that is essential across all three domains of life and is responsible for activating a wide range of primary and secondary metabolic pathways. Such pathways include the biogenesis of essential fatty acids, polyketides and non-ribosomal peptides that serve as virulence factors in pathogenic bacteria. Phosphopantetheinyl transferases (PPTases) covalently attach the pantetheine (4'-PP) cofactor group to their recipient carrier proteins (CPs). CPs then carry the metabolic intermediates, covalently tethered to the long and flexible 4'-PP arm, from one reaction centre to the next. Pantetheine attachment by PPTases is thus essential for the activity of key biosynthetic pathways and ultimately for the viability of the organisms. This research focused on PPTases from two pathogenic bacteria, AcpS and PptT from Mycobacterium tuberculosis (Mtb) and PcpS from Pseudomonas aeruginosa (Pa), and on selected CPs (MbtL, PpsC and AcpM) from Mtb. Structural and functional studies have been carried out to aid in developing selective inhibitors of these bacterial PPTases.

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  • Weighted likelihood and calibration for countermatched designs

    Rivera Rodriguez, Claudia (2015)

    Doctoral thesis
    The University of Auckland Library

    The use of all information available on an entire cohort when fitting Cox models can be limited due to exposures of interest available only in a sample. If a case- cohort design is used, the standard estimation method (pseudolikelihood) allows for methods from survey sampling, such as calibration, to be used in order to take advantage of auxiliary information. However, under countermatching designs, the standard estimation method (partial likelihood) utilizes only one variable on the entire cohort and it does not admit the use of calibration. In this dissertation, calibrated weights are applied to countermatched designs. The calibration variables are an approximation of the influence functions of the estimator. The methods are evaluated through simulations for models with time- fixed and time varying covariates. Situations in which countermatching can be preferred over case -cohort or matching are considered. These situations include the case when a rare exposure is available for the sample, but there is a surrogate of this on the cohort. Countermatching on the surrogate leads to more efficient estimates. The new method is compared to partial likelihood and pseudolikelihood with standard weights under different designs (matching and case -cohort). Pseudolikelihood with calibrated weights returns more efficient estimators than the other methods in most situations, particularly for coeffi cients whose variables are available on the entire cohort. Partial likelihood can be more efficient than pseudolikelihood in the presence of confounding variables in the model or for variables that are unrelated to the countermatching variables. However, calibrated weights can recover the efficiency lost if suitable auxiliary information is available. The efficiency of the methods under misspecified models is also discussed. Pseudolikelihood is a more suitable method if the interest is to estimate the cohort coefficients. Furthermore, asymptotic normality of pseudolikelihood estimators with both standard and calibrated weights is discussed using an empirical processes approach. The result is attained for time -fixed Cox models. A potential information bound for under the missing at random assumption in two -phase sampling designs is studied and compared to the proposed methods .

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  • Human Adenoviruses As Indicators Of Faecal Contamination And Pathogen Indices In The Environment And Shellfish

    Hewitt, Joanne (2015)

    Doctoral thesis
    The University of Auckland Library

    The main aim of this study was to assess the use of human adenoviruses (HAdVs) as occurrence indicators of human enteric viruses in the environment and shellfish. The second aim was to consider human polyomaviruses (HPyVs) for the same roles. To gain a better understanding of the ecology of HAdV, their diversity in the environment was also investigated. Method development included validation of an ultrafilter for virus concentration from water samples; real-time quantitative PCR (qPCR) assay development; evaluation of culture-qPCR using different cell lines; and assessment of guanidine hydrochloride to inhibit enterovirus growth in virus quantification assays. The presence, quantity, and where possible, infectivity (using HEK-293 cells in a culture-qPCR assay with guanidine hydrochloride) of HAdVs were determined in a range of environmental samples and shellfish. The presence and quantity of HPyVs, noroviruses and enteroviruses were also determined where appropriate. HAdVs, predominantly species F and other HAdV species at lower concentrations, were frequently present in high concentrations in wastewater influent, independently of wastewater treatment plant size. They were also present in non-disinfected effluent irrespective of treatment type. HPyVs were prevalent at concentrations at least as high as HAdVs in wastewaters. In biosolids, the occurrence of HAdVs and HPyVs were comparable to enteroviruses and like wastewater, were detected more frequently than noroviruses. In urban streams, rivers and estuaries, neither HAdVs nor HPyVs were dominant in terms of their occurrence and so should be used as part of a multi-tool source tracking system. Shellfish studies showed a low occurrence of HAdVs and HPyVs, probably due to poor virus recovery. Further studies are required to investigate this. The results of this study strongly supported the hypothesis that HAdVs and HPyVs are suitable indices for viral contamination from faecal sources. Furthermore, due to their continued occurrence in the environment and their host specificity, these viruses also have potential for microbial source tracking applications. However, one caveat identified was the difficulty in recovering HAdVs, and presumably HPyVs, from shellfish. In conclusion, although it is unlikely that the detection of a single indicator by one method will be sufficient to identify health risks and faecal contamination sources, HAdVs and HPyVs together are a good option for viral indicators of faecal contamination and as pathogen indices in the environment.

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  • Eliciting and analysing perceptions of prosodic prominence: a Maori case study

    Thompson, Laura (2015)

    Doctoral thesis
    The University of Auckland Library

    This project outlines a methodology developed for analysing perception of prosodic prominence based on M??ori, the indigenous language of New Zealand. Development of the study began with a pilot, which employed a perception test involving a recorded tapping exercise. The second phase implemented a participant-friendly, purpose-built web survey, increasing efficiency and accessibility. The third phase increased the scale and developed a statistical processing method for determining significantly perceptually prominent syllables (PPMs) based on the perception test responses. Ninety-two New Zealand and overseas listeners responded to 30 short recordings of continuous M??ori speech from the MAONZE database (King et al., 2011a). Since native language cues affect prominence perception in any language, participants were further divided into three self-rated M??ori proficiency groups. Results indicated a pattern of difference between high proficiency and lower or zero proficiency participants, both in response to the perception task, the effects of which were handled by the result-processing, and in PPM identification, though the latter difference was not always significant. Analysis of PPMs from all groups indicated strong alignment with syllables where existing expected phrase and word stress overlap, and with word stress (but not phrase stress) alone; a sensitivity to heavy (2+ morae) syllable weight and whole syllable duration; and influence from F0 movement around the phrase F0 peak or from the F0 peak itself. There were indications that the strongest prominence effect is cumulative, but that word stress cues are, or have become, stronger than phrase stress cues, and that this may be increasing with time.

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  • Mana Moana: Wayfinding and Five Indigenous Poets

    Sullivan, Robert (2015)

    Doctoral thesis
    The University of Auckland Library

    This thesis identifies diverse indigenous worlds in the published poetry of five first and second wave Pacific writers from the Moana Nui a Kiwa: Samoa, Aotearoa (Te Tai Tokerau, and Te Waipounamu), Cook Islands (Tongareva), and Hawai??i (Kaua??i and M??ui). Together they form a literary constellation by which I (and many others) have navigated my way as a ???writer-scholar??? (Winduo). In order to chart these worlds, this thesis bases its critical approach in the Moana, the ocean beyond the reef (Pollex), and articulates a wayfinding kaupapa as a close reading method. Wayfinding is used to identify/chart the identity assertions, cultural signs, re-told narratives, linguistic and social references in the poetry of these writers, as well as the principal relationships deduced from published interviews and recordings, and unpublished layers within available archives. Wayfinding enables a Pacific-centric navigation through these Moanan worlds. It focuses on an indigenous frame of reference. The term ???Moanan??? is used in the context of maintaining sociospatial connections - what Ka???ili refers to as the ???Tauhi V????? (92). To be Moanan then is to occupy and maintain the connections between such transnational and indigenous spaces of relationship, also formulated as the ???v????? (Ka???ili 89, 92). This identity is uniquely formed throughout each poem and each poet???s oeuvre (life-work); each author brings different sets of relationships and histories to their writing. These differences make the identity assertion necessarily porous and fluid, akin to Kamau Braithwaite???s idea of ???tidalectics??? as developed by Elizabeth DeLoughrey in an investigation of ground-based and ocean-based discursive modes, or ???roots??? and ???routes??? in her comparative study of Caribbean and Pacific Literatures. In a Moanan world, the reef ??? a liminal zone???is a fecund and porous barrier used to navigate through and hover over the signs of the texts through close reading. This thesis reads these as ???reefs of literary production???, a modification of Bourdieu???s formulation of the field of cultural production, in order to chart the life-worlds of these texts, in addition to using related strategies drawn from a range of intellectuals and discourses inside and outside the Moana. A number of tropes are explored as modes of inquiry and are used to identify relationships between people, times and locations. These include the k??puka, the v??, waka navigation, and deified representations of significant natural features including Tangaroa/ Tagaloa/ Kanaloa, Pele, and Papat????nuku/ Papahanaumoku. Aligned with symbolic or figured worlds, the senses and the body are also important. This accumulation of discourses and symbols is likened to traditional wayfinding techniques, particularly that of ???expanding the target??? (Howe, Diaz) in which general locations are deduced from a range of referents. The traditional techniques rely on memory as knowledge, and recourse to the signs available in the natural world, whereas contemporary navigation relies on instruments and two dimensional charts. Through a similar indigenous navigational and holistic technique, a heterogeneous site (akin to Epeli Hau???ofa???s sea of islands) is claimed for multi-layered streams of Moanan poetics in English within the works of the five poets. This is not claimed as an exclusive identity formation, as other formations indeed sit alongside/ entangle/ interweave/ flow within Moanan identities such as other racial, sexual preference, gender, and class formations. Rather, this thesis argues that this Moanan wayfinding Pacific-centric close reading technique makes possible the charting of five diverse indigenous worlds, five distinct oeuvres of poetry that derive energy from Moanan identities and ritenga tangata or culturally inherited ways of being.

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  • Te Ru Tamariki: A Study of Juniors Settling into School and Learning: Parent Report

    Liberty K; Macfarlane S; Hooper L; Allan, M (2015)

    Reports
    University of Canterbury Library

    In our study we are looking at how children cope with stress in their daily lives, especially during their time at school. To date, our has study shown that while some children are more resistant to stress, other children are sensitive to changes in their surroundings and find it difficult to cope with stress. This sensitivity to stress is likely to be caused by the children’s exposure to many unsettling earthquakes before they were four years of age. We have found an increase in the number of children who have difficulty feeling settled in the classroom, compared to our pre-earthquake study, which is probably due to their earthquake related experiences. This means that some children might be irritable at school and feel nervous or tense and as a result, they may have difficulty in controlling their temper and expressing themselves in a positive and pro-social way. This stress reaction might also be getting in the way of their learning. They are not behaving this way on purpose. These children are sensitive to stress and it is more difficult for them to develop positive coping strategies.

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  • ???Framed in Righteousness???: Poetry, imagination and edification in early modern England 1530-1630

    Fox, John (2015)

    Doctoral thesis
    The University of Auckland Library

    My thesis attempts to trace the theological language of building (???edification???) from its use by Thomas Cranmer and other English reformers through the maelstrom of the English reformation from 1530-1630. I argue that the language of edification, with its emphasis on communitarian re-formation and the transformative effects of an encounter with truth, offers a new way of seeing the vocation of the Protestant poet within the imaginative and spiritual conflicts that shaped the English reformation. I trace the language from its origins in Pauline thought to the English reformers, and from them to the poets and writers who internalised their vision of Pauline Commonwealth: Philip Sidney, Edmund Spenser, George Herbert and John Donne. Arguing that edification enables both deconstructive and reconstitutive kinds of reform, I examine the imagined role of poetry in that process of ???rebuilding??? the person, and the differing responses to, and re-imaginations of the notion of rebuilding.

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  • Neuroprotective potential of AAV-mediated NURR1 expression in a rat model of Parkinson???s disease

    Mudannayake, Janitha (2015)

    Doctoral thesis
    The University of Auckland Library

    Parkinson???s disease (PD) is characterised by the progressive neurodegeneration of the nigrostriatal dopaminergic neurons that results in motor deficits including bradykinesia, rigidity and tremor. Currently available pharmacological therapies for PD provide only symptomatic relief, and hence lead to therapeutic failure in the advanced stages of the disease. Gene therapy that targets the underlying disease mechanisms is an appealing alternative strategy to ameliorate disease progression. Adeno-associated viral (AAV) vectors are currently the preferred gene delivery vehicles in clinical gene therapy applications. To date, clinically-approved AAV vectors for CNS gene therapy almost exclusively target neurons, and astrocytes that regulate CNS physiology and contribute to disease pathogenesis represent a largely unexplored therapeutic target. Therefore the aims of this thesis were to develop an AAV vector that selectively and efficiently target nigral astrocytes by coupling astrocyte-tropic AAV serotypes and DNA promoter elements, and subsequently utilise this vector to overexpress the therapeutic transcription factor NURR1in a rat model of PD. Recent evidence suggests that astrocytic molecular diversity may heterogeneously regulate transcriptional activity of the commonly used astrocyte-specific glial-fibrillary acidic protein (GFAP) promoter, prompting us to isolate putative promoter sequences from the recently characterised pan-astrocytic marker aldehyde dehydrogenase family 1, member L1 (ALDH1L1), to determine the ability of these promoters to efficiently regulate transgene expression in astrocytes. Four promoter sequences were generated and tested in the context of the astrocyte tropic AAV serotypes 5, 8 and 9 in the rat substantia nigra pars compacts (SNpc). Unexpectedly, these promoters mediated exclusive and efficient neuronal transgene expression, indicating the potential applicability of these promoters in neuronal-targeted gene therapy. In a subsequent comparative analysis of AAV5 and AAV9, AAV5 that predominantly targeted astrocytes in the nigra with minimal dissemination of transgene expression to neighbouring midbrain regions was selected for further studies. Moreover, comparative analysis of the promoters, constitutively active cytomegalovirus (CMV), GFAP and shorter GFAP variant gfaABC1D in the context of AAV5 indicated that the GFAP promoter mediated the most efficient transgene expression predominantly in nigral astrocytes. Therefore, the GFAP promoter in the context of AAV5 was selected to mediate efficient transgene expression in astrocytes. Using this vector construct, the multifaceted transcription factor NURR1 that regulates midbrain DA neuronal phenotype, and downregulates glia-driven inflammation was selectively expressed in astrocytes to determine the neuroprotective potential of astrocyte-targeted gene therapy. NURR1 overexpression promoted nigral DA neuronal survival, ameliorated astrocyte reactivity, and improved contralateral forepaw deficit, indicating therapeutic potential of astrocyte-targeted gene transfer. These results support the development of a dual cell targeting AAV vector in future studies for the expression of NURR1 in both neurons and astrocytes to target DA phenotypic dysfunction, chronic inflammation and neurodegeneration in PD.

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  • Reactions and phase transformations in Monocalcium Phosphate Monohydrate (MCPM) systems

    Huang, Chen (2015)

    Doctoral thesis
    The University of Auckland Library

    This research project mainly focuses on the characteristic reaction processes and phase transformation (transition) in the system of monocalcium phosphate monohydrate (MCPM, Ca(H2PO4)2???H2O) ??? base and covers two types of reactions: aqueous reactions and solid-state reactions. Firstly, a preliminary research, which deals with the influences of the reaction conditions, such as pH, pH buffer reagent, ageing and stirring, in the MCPM ??? base system has been carried out. It is found that pH is a key factor determining the phase formation. As the pH level increases, the sequence of the phase formation from precipitation reaction is from dicalcium phosphate dihydrate (DCPD, CaHPO4???2H2O) to calcium-deficient (hydroxy) apatite (Ca10-x(HPO4)x(PO4)6-x(OH)2-x, 0 < x ??? 1) and finally to stoichiometric apatite. The pH buffer reagent, such as NaOH or NH3???H2O, is also an important factor with respect to the determination of the precipitated phase. A strong base, for example NaOH, promotes the formation of apatite with higher stoichiometry, in comparison with a weak base, such as NH3???H2O. The micro-morphology of apatite precipitated from NaOH is more homogeneous than that of apatite formed from NH3???H2O. The MCPM ??? NaOH is therefore set as the research system onwards. In addition, ageing is essential to the phase maturation of apatite, which is then extensively explored in the MCPM ??? NaOH system. Also stirring is deemed to accelerate the reaction process. Based on the preliminary results, the MCPM ??? NaOH system, both aqueous reactions and the subsequent solid-state reactions have been separately investigated. In the study of aqueous reactions, a continual change of Ca:P ratio in monocalcium phosphate monohydrate (MCPM) by increasing the amount of NaOH added in to the MCPM is reported. The Ca:P ratio is observed to gradually change from 1.0, which corresponds to dicalcium phosphate dehydrate (DCPD), to stoichiometric 1.67 of apatite. It is proposed that the high solubility of MCPM results in fast dissolution and reprecipitation. A multi-step chemical reaction is proposed to elucidate the reaction sequence in the aqueous MCPM-NaOH system. The Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation is applied to the kinetic study. The phase transformation of MCPM to apatite has been accelerated by increasing the NaOH molarity. The high solubility gives MCPM the ability of fast dissolution and reprecipitation. Chemical reactivity and sensibility of MCPM towards base (NaOH) has been verified. Based on the dissolution-reprecipitation mechanism, a model to elucidate the microstructural evolution is proposed. Depending on the attained Ca:P ratio in the powder synthesized in the aqueous solutions, subsequent calcination of these chemically formed powders leads to the formation of various single phasic calcium phosphates or biphasic compounds. It is observed that ??-calcium pyrophosphate (??-CPP, ??-Ca2P2O7) is produced from calcination of DCPD, while ??-tricalcium phosphate (??-TCP, ??-Ca3(PO4)2) results from thermal reactions between DCPD and apatite. The biphasic mixtures of ??-TCP and hydroxyapatite (HA, Ca10(PO4)6(OH)2) can be achieved from thermal decomposition of calcium-deficient apatite. The phase composition of ??-TCP/HA biphasic calcium phosphate is determined by the calcium-deficiency of apatite. The more calcium-deficient the apatite is, the more ??-TCP exists in the biphasic compound. The kinetics of the thermal decomposition process of calcium-deficient apatite is characterised using the JMAK equations. The thermal behaviours of calcium-deficient apatite with different calcium-deficiencies have been compared. It is discovered that the more calcium-deficient the apatite is, the faster the decomposition. This is explained by the vacancy mechanism of diffusion in solids. The sinter-ability of ??-TCP/HA biphasic ceramics with two different phase compositions has been examined. It was revealed that the formation of more ??-TCP is detrimental to the densification of the biphasic ceramics during sintering. Several characterization techniques have been used throughout the project. They include powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray fluorescence (XRF), thermogravimetric analysis (TGA), transmission electron microscopy (TEM), selected area electron diffraction (SAED), high-resolution transmission electron microscopy (HRTEM), high angle annular dark field (HAADF) imaging under scanning transmission electron microscopy (STEM), scanning electron microscopy (SEM) and cryogenic transmission electron microscopy (Cryo-TEM).

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  • Dynamic testing and model updating of an eleven-span concrete motorway bridge

    Chen, Gewei (2015)

    Doctoral thesis
    The University of Auckland Library

    In recent decades, the evaluation of the actual behaviour of in-service bridge structures and their safety throughout their life cycle, by measuring structural responses, has been attracting increasing research efforts worldwide as an alternative to visual inspections or localised nondestructive tests. The vibration-based structural health monitoring methodology is a representative approach, based on the direct relationship of stiffness, mass and damping to the modal properties of a structure. Dynamic properties can thus be used to determine deterioration, damage, or change in structural state. For instance, the reduction in natural frequencies is the most easily observable change in the modal data and investigators have linked it to various structural deterioration mechanisms. However, real-world bridges are exposed to time-varying environmental and operational conditions such as changes in temperature as well as vibration level, which can influence the variability of modal parameters. These effects must be understood and quantified so that changes in vibration response resulting from damage can be discriminated from changes resulting from other factors. There is an abundant literature concerned with the effects of temperature on modal parameters, the quantitative relationships between temperature and modal properties, and data normalisation to account for environmental variability. However, comprehensive explorations of the influence of vibrational magnitude on the variability in dynamic characteristics of bridge structures are limited, because this operational variable is difficult to control in situ. In this research, in order to experimentally identify the amplitude-dependent properties of a bridge, a series of steady-state harmonic forced-vibration tests with different forcing levels were undertaken on the Nelson Street off-ramp bridge, an eleven-span, post-tensioned concrete motorway bridge located in Auckland, New Zealand. Both the natural frequencies and the damping ratios were identified from a series of frequency response functions constructed at different levels of excitation, and were subsequently quantitatively correlated with the displacement amplitude. The influence of vibration response amplitude on bridge structure damage detection was studied by comparing the calculated frequency shifts caused by the damage simulated on a beam element girder numerical model of the bridge with the experimental amplitude-dependent frequency data. Accurate identification of the dynamic characteristics of the monitored bridge structure from the collected response data by using modal parameter identification techniques is essential for obtaining reliable evaluation results by using dynamic-based condition assessment methods. Unfortunately, unlike the ideal test environment in a laboratory, external disturbances and elevated sensor measurement noise is unavoidable at an outdoor testing site, which poses great challenges to extracting weakly excited modes from noisy data in ambient vibration testing. The important issue of the feasibility and reliability of the dynamic tests under the circumstances of relatively weak excitation has rarely been investigated in detail. In this thesis a set of dynamic tests with different excitation sources, which included environmental sources, people jumping, broad-band linear chirp excitation induced by electro-dynamic shakers, and sinusoidal sweeping excitation by eccentric mass shakers, were conducted on the motorway bridge. The mode identifiability, and the accuracy of modal properties identified from relatively weak excitation cases were studied through comparison with a large-capacity shaker excitation case at strong forcing level. In order to investigate the ability of different identification algorithms to capture signal characteristics from the noise contaminated response data, various operational modal parameter identification algorithms in the frequency domain (the peak picking and the frequency domain decomposition methods) and the time domain (data-driven stochastic subspace identification method and Eigensystem realisation algorithm) were employed to extract natural frequencies, damping ratios and mode shapes for each excitation case. Cross-validation between different identification techniques was carried out to determine their efficiency, robustness and accuracy. Finite element (FE) updating, in which the physical parameters of a FE model are calibrated to match the measured modal properties of the structure, also plays a significant role in vibration-based condition assessment, because the updated model parameters can be used to trace the evolution of stiffness deterioration. However, due to the unique characteristics of bridge structures, such as their large size, soil-structure interaction, complex structural member connections as well as uncertain material properties and boundary conditions, hindrances can be encountered to solving the updating problem in highly nonlinear solution spaces, as is the case for real-world bridges. For the present analysis, relatively large differences were observed in the natural frequencies and mode shapes between the results calculated from even a very detailed initial shell-element numerical model of the bridge and the field vibration testing results, due to the complex and uncertain boundary conditions. Manual model refinements through tuning the connection stiffness between the main girder and piers/abutments were proposed for reducing the modelling errors of the initial FE model. Then, two different types of non-linear optimisation algorithms, the subproblem approximation method (SAM) and the first order method (FOM), were utilised to further update the manually tuned FE model. The initial attempt of the FOM captured a local minimum. After the initially assumed values of the updating parameters were perturbed, the FOM was rerun. The consistency of the final FE model updating results between the two methods enabled confirmation of the updating results.

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  • An Abstract Micro Simulation of Gentrification: A case of Point Chevalier, Auckland

    Liu, Cheng (2015)

    Doctoral thesis
    The University of Auckland Library

    This research describes a simple, abstract model to simulate gentrification from both supply and demand side perspectives. Three theories???rent gap theory, filtering theory and household life cycle theory???are employed to construct a combined cellular automaton and agent-based model. The model exhibits a distinctive relationship between the spatial dynamics of gentrification patterns and different rent gap thresholds: at low rent gap thresholds, renovation events occur at all locations leading to a mixed rental map distribution. As the rent gap threshold increases, gentrification becomes more spatially concentrated, leading to spatially segregated rental patterns. Meanwhile, depending on both household entry and exit probabilities and the rent gap threshold, household income distributions exhibit diverse patterns: scattered and mixed at the low rent gap threshold through to segregated at a high rent gap threshold. The abstract gentrification model is evaluated against the spatial gentrification pattern at a Point Chevalier (inner Auckland) study area. Local spatial association analysis suggests that the dynamics of local gentrification in Point Chevalier mirror those of the model at a low threshold rent gap, substantiating the model???s credibility, at least in this study area. This study indicates that a different threshold rent gap is able to lead to either a mixed or segregated rental pattern. This provides a possible explanation of the dissonance in the empirical spatial gentrification pattern ??? some scholars observe intensified segregation after gentrification, while others do not.

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