27,372 results for ResearchSpace@Auckland

  • High-frequency Power Conversion and Variable Capacitor Control for IPT Systems

    Tian, Jianlong (2017)

    Doctoral thesis
    The University of Auckland Library

    Wireless Power Transfer (WPT) technology can be dated back to more than 120 years ago with some early work by Tesla. However, practical modern WPT technologies only started in the late 19th century with the invention of high-frequency power electronic devices, which made possible the generation of high frequency voltages and currents efficiently with switch mode power converters. High frequency operation is a prominent feature and essential requirement of WPT systems compared to traditional tightly-coupled transformers and electric machines because of the loosely-coupled nature between the primary and secondary sides of WPT systems. To generate the high frequency voltages and currents for WPT systems, switch mode DC-AC power converters are usually employed, and they are preferably soft-switched for resonant operation in order to maximize the system efficiency and minimize EMI (Electromagnetic Interference). This research aims to explore new methods to control the operating frequency of WPT systems. Based on the investigation of different types of high frequency resonant converters, including current-fed energy injection converters, Class E, and autonomous push pull converters, this thesis proposes a DC-voltage Controlled Variable Capacitors (DCVC) to dynamically control the zero voltage switching (ZVS) frequency of autonomous push-pull resonant converters for adjusting or stabilizing the operating frequency, and regulating the power flow to keep the output voltage constant. The equivalent capacitances of DCVCs are varied by controlling the conduction period of a diode in parallel with part of the tuning capacitors of the proposed circuit. In this research the conduction period of the diode is controlled by a DC voltage through two different measures via a bias circuit including a resistor (R-DCVC), or a transistor (T-DCVC). Unlike conventional switch mode capacitors, the proposed DCVCs are controlled smoothly by a DC voltage, so they are more suitable for high frequency operation. In addition, because there are no active switching and related gate drive issues, the EMI (Electromagnetic Interference) of the system can be greatly reduced, and more accurate control can be achieved compared to full switch mode counterpart. The proposed DCVC method and its detailed operation for different applications are fully analysed in theory, and verified by simulation and experimental results. Both the R-DCVC and T-DCVC methods have been applied to adjust the ZVS frequency at the primary side of IPT systems. A PLL controller is designed to stabilize the operating frequency of an IPT system while maintaining soft switching conditions, which helps to simplify the pickup circuit design, particularly with multiple power pickups. It has demonstrated that using the proposed DCVC method the operating frequency of an IPT system can be varied or stabilized in the range of a few hundred kHz to tens of MHz. The T-DCVC is also applied at the secondary side of an IPT system as a series or parallel tuned variable capacitor to regulate the power flow to stabilize the output voltage against the magnetic coupling and load variations. A prototype circuit at about 10W has been built and the experimental results have shown that the output voltage can be stabilized in the range of 5V to 24V with an accuracy of 2%, which is sufficient for driving most low power consumer electronic devices.

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  • Effects of Sn and Pb Additions on Microstructures and Mechanical Properties of As-Cast, Rolled and Annealed AZ61 Magnesium Alloys

    Hou, Haibo (2017)

    Doctoral thesis
    The University of Auckland Library

    Magnesium (Mg) alloys are promising structural metallic materials owing to their low density and high specific strength. Mg alloys have been used in many industries including aerospace and vehicle parts, and portable electronic devices, where weight saving is of crucial importance. Researchers around the world are engaged in improve the mechanical properties of Mg alloys with various approaches, such as alloying, heat treatment, and deformation process. Among Mg alloys, AZ series (Mg-Al-Zn) Mg alloys possess suitable corrosion resistance, castability, and relatively satisfied mechanical properties. Compared to AZ31 and AZ91, AZ61 can be used in the forms of both as-cast state and the deformed state. In addition, AZ61 alloy possesses moderate strength and ductility. Further improvement of the mechanical properties by introducing the rare earth elements increases the cost of the production. In this study, in order to improve the mechanical properties of AZ61 Mg alloy, Sn (tin) and Pb (lead) were selected as alloying elements to modify the microstructures and mechanical properties of as-cast and rolled AZ61 Mg alloys. Certain amounts of Sn or Pb element were added as the alloying materials for the casting of AZ61 alloys. With the introducing of Sn or Pb elements into the AZ61 alloy system, the modification in phase and morphology of the intermetallic phases were examined. The mechanical properties, including wear resistance, hardness, and tensile properties, were tested and analysed. The experiments and results are summarized as follows: (1) Different amounts of Sn alloying addition were managed to add into the AZ61 Mg alloy by using the high induction furnace. The XRD (X-Ray Diffraction) result and the optical microstructures indicate that primary ??-Mg phase, eutectic ??-Mg phase, divorced eutectic ??-Mg17Al12 phase, and lamellar ??-Mg17Al12 particles were formed in as-cast AZ61-Sn alloys. Moreover, Mg2Sn phase was found to coexist with Mg17Al12 phase in AZ61-3Sn and AZ61-5Sn alloys. SEM (Scanning Electron Microscope) examination indicated that Sn increased the elemental segregation, refined the dendrites and decreased the average grain sizes. The enhancement of wear resistance and hardness was observed in Sn-containingAZ61alloys. The yield strength of the alloy was improved with the increasing addition of Sn owing to the formation of Mg2Sn precipitates and refined average grain sizes. However, an exceeding amount of Sn addition leads to the decrease of the UTS (Ultimate Tensile Strength) and elongation because of the continuous distribution of the intermetallic compounds. Furthermore, the Sn addition has changed the fracture mode of as-cast AZ61 alloy from transgranular fracture to intergranular fracture. (2) As-cast AZ61-Pb alloys were prepared by the high vacuum induction furnace to study the effect of Pb addition on the microstructure and mechanical properties. The XRD result suggested that Pb alloying did not change the kinds of phases in as-cast AZ61 alloy, which is attributed to the large solubility of Pb in Mg. The elemental distribution of Pb in as-cast AZ61 alloy was studied through EDS (Energy Dispersive Spectrometer). Results showed that Pb inclined to exist in the interdendrites rather than in the dendrites, and preferred to segregate in the ??-Mg phase rather than to exist in eutectic ??-Mg17Al12 phase. The wear resistance and the hardness were improved slightly due to the solid solution strengthening effect. Pb also leads to the increase of yield strength. However, the tensile properties decreased with excess Pb additions due to the variation of morphology. The fracture mode of the as-cast Pb added AZ61 alloys remained as the transgranular feature. (3) Rolling deformation was applied on the homogenized AZ61-Sn alloy. The inter-pass annealing temperature is 340??C and 400??C respectively. The alloy samples were rolled with the total thickness reduction of 50% and 80%, followed by cooling in air. The microstructures of the rolled alloy were replaced with a large number of deformation twins. With increasing addition of Sn, the fraction of the deformation twins tended to rise after the rolling process. Another significant finding in the rolled AZ61-Sn alloys is that the fine precipitates of Mg2Sn phase were occurred. Subsequent isothermal annealing treatment was performed to release the residual work stress. The annealed alloys showed equiaxed grains owing to the static recovery and recrystallization. The grain growth was suppressed in the Sn-containing alloys with Mg2Sn precipitates. The mechanical properties of the rolled and annealed alloy were tested. The wear resistance, hardness, yield strength and UTS were increased with Sn additions due to the precipitation hardening, work hardening, and grain refinement effects. However, the elongation decreased with Sn addition in the rolled and annealed AZ61 alloys. (4) AZ61-Pb alloys were homogenized and rolled to a final reduction rate of 80% with the inter-pass annealing temperature of 400??C. The results showed that the Pb alloying element increased the fractions of twinning structure in the rolled AZ61 alloys. The isothermal annealing treatment was performed after rolling. The microstructures of the annealed alloys revealed equiaxed grains rather than the deformation twins owing to the static recovery and recrystallization. The average grain sizes of the annealed AZ61 alloys were decreased with 0.5 wt.% Pb addition. However, excessive additions of Pb result in the coarsening of grains. The wear resistance of Pb added AZ61 of rolled and annealed state were decreased. However, the hardness, yield strength and the UTS were generally enhanced by the Pb addition. The elongation of the rolled state was improved by Pb addition, while that of the annealed state was decreased. In summary, by introducing the alloying additions of Sn or Pb to AZ61 Mg alloy system, the microstructures and mechanical properties of the as-cast, rolled and annealed alloys have been evaluated systematically. Sn alloying formed Mg2Sn phase in the as-cast AZ61 alloy, while Pb alloying did not change the kinds of phases in the system. The yield strength was improved with Sn addition due to the hard Mg2Sn particles. However, the UTS and elongation were slightly decreased owing to the coexistence of Mg2Sn and Mg17Al12 particles. Pb addition generally increased the strength and decreased the elongation in AZ61 alloys. The rolling deformation and subsequent annealing treatment endowed even better mechanical properties to AZ61 alloy by Sn and Pb additions, such as very high yield strength and UTS. Notably, the significant enhancement in strength of the Sn added alloys was achieved due to the existence of the precipitation after deformation. The possible strengthening mechanisms include the solid solution strengthening, precipitation strengthening, work hardening, and grain refinement strengthening. Meanwhile, the Pb addition generally improved the yield strength and UTS due to the solid solution strengthening. Furthermore, the ductility of rolled state AZ61 alloys was enhanced by Pb alloying.

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  • 3D Printed Conducting Polymer Microstructures as an Ultra-low Velocity Flow Sensor

    Devaraj, Harish (2016)

    Doctoral thesis
    The University of Auckland Library

    To develop devices for improving the quality of life such as handheld electronics, artificial muscles, lab-on-chip devices, etc., the quest for future smart materials has led to increasing interest in Conducting Polymers (CPs). Recent technological advancements have already exploited the many advantages of CPs, but to further their usability, we require a reliable and robust means of fabricating CPs at micrometric scales. This research work focusses on demonstrating these fabricated CP micro-structures??? applicability in biomedical applications and, more specifically, as a means of sensing and measuring air flow levels observed during neonatal resuscitation. In this thesis, I present a reliable means of fabricating three-dimensional CP microstructures, in particular focusing on fabricating hair-like microstructures from Poly(3,4-ethylenedioxythiophene) Poly(styrene sulfonate), referred to as PEDOT:PSS. A 3D printer was developed with capabilities of producing microscopic patterns and structures using miniaturized pipettes for dispensing the CP material. A Graphical user interface was also developed to allow human interface with the microstructure printer. A novel flow sensor prototype was developed using PEDOT:PSS micro-hairs, where these micro-hairs act as microscopic switches which open and close in response to air flow. By using an array of micro-hairs that respond to specific flow velocities, a discrete digital output flow sensor was demonstrated. A means of improving the sensitivity of the flow sensor to lower flow velocities was also demonstrated by printing the micro-hairs within a narrow convergent-divergent flow channel. To improve the understanding of the flow sensor???s response to air flow by simulating the Fluid-structure interactions (FSI), a robust mathematical model was developed. Based on Lattice Boltzmann equations for simulating the fluid flow in a 3D domain and beam theory for simulating large deflections, the model was exclusively coded in MATLAB. Using dimensional transformations to minimize the computational costs, a mixed 2D and 3D simulation for the developed FSI model is presented. Using the FSI model, a final sensor prototype was developed specifically to be compatible with the target neonatal resuscitator device. Apart from being capable of measuring the ultra-low velocity flows experienced during neo-natal resuscitation to meet the demands of the target application, this prototype sensor was designed to be portable with the capability of reading out flow levels directly integrated with the sensor. Furthermore, the portable sensor was also developed with a disposable architecture to improve medical compatibility. By successfully demonstrating the capabilities of fabricating CPs in micrometric scales and using these microstructures as a suitable means of sensing air flow through the development of an ultra-low velocity flow sensor, the suitability of using CP microstructures in real world applications has been demonstrated.

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  • Feed the people and you will never go hungry: Illuminating Coast Salish economy of affection

    Kelly, Darlene (2017)

    Doctoral thesis
    The University of Auckland Library

    This thesis explores the nature of Coast Salish economy of affection through related concepts of wealth, freedom and unfreedom in Canada with the prospect that a better understanding of these concepts will enhance contemporary and future approaches to economic development that emerge out of Coast Salish values. Economic unfreedom emerged with introduction of the Potlatch Ban, and its residual impacts are prevalent today as discussed in X??:m! Crying, weeping???the affective expression of grieving that shapes how the Coast Salish wisdom keepers in this research talk about gatherings. Economic freedom from within Coast Salish worldview is inherently spiritual by virtue of the interrelated nature of exchange between X??:ls, the Creator, S??lh T??m??xw, the river environment, and Xw??lmexw, the river people. The author offers a theoretical exploration using the Capability Approach of the extent to which Coast Salish freedom depends on the removal of residual economic unfreedom for t??miyeqw, the seven generations of unborn Coast Salish people. This thesis makes a methodological contribution through the use of autoethnography, oral history and heuristic inquiry as a research methodology that places Coast Salish philosophies of knowledge transmission at the centre, by listening to the voices of the ancestors through their descendants. The research contextually explores Coast Salish economic capability embedded within the ceremonial institution of gatherings including: access to wealth founded in syew??:l, genealogy and S??wes, knowledge from the Teachings; having the ability to conduct spiritual ???work??? in ceremony; engaging in spiritual exchange with X??:ls, the Creator and ancient ancestors; and creating relationships through gifting, debt, saving and banking that weave Coast Salish people together in a continuous selfsustaining network of interdependence. Coast Salish freedom is expressed in gatherings facilitating exchange within and across a complex interplay of spiritual, environmental, socio-cultural and financial capabilities. This expression of Coast Salish economic freedom allows for becoming a whole person and whole peoples within an economy that encapsulates all aspects of spiritual, environmental, socio-cultural and economic capability. It is an economy of affection in which Coast Salish individuals and peoples are wholly seen and recognised.

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  • An assessment of the Hauraki Gulf Cableway Protection Zone (CPZ), relative to adjacent seafloor

    Morrison, M; Tuck, Ian; Taylor, Richard; Miller, A (2016-02)

    Report
    The University of Auckland Library

    The Hauraki Gulf Cable Protection Area is a mapped corridor where fishing and anchoring is prohibited, protecting a major international communications cable. This report describes an ecological survey of the cable protection area and assesses impacts on seafloor communities.

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  • Feasibility study for EEZ-scale Marine Trophic Index

    Pinkerton, M; Tuck, Ian (2016-06)

    Report
    The University of Auckland Library

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  • Characterisation and length-based assessment model for scampi (Metanephrops challengeri) in the Bay of Plenty (SCI 1) and Hawke Bay??? Wairarapa (SCI 2)

    Tuck, Ian (2016-10)

    Report
    The University of Auckland Library

    Assessments of SCI 1 and SCI 2 stocks have been updated, and both were accepted. For SCI 1, SSB remains stable at around 75% SSB0. Fishing intensity has consistently been below F 40% B0. For SCI 2, SSB has continued to increase, and is between 89% and 113% SSB0. Fishing intensity peaked in 2002 but has declined in recent years, while SSB/SSB0 has increased. For both stocks, future catches up to 156 tonnes (SCI 1) or 200 tonnes (SCI 2) to 2021 are not predicted to reduce the SSB below 40% SSB0.

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  • Characterisation and a length-based assessment model for scampi (Metanephrops challengeri) on the Mernoo Bank (SCI 3)

    Tuck, Ian (2016-10)

    Report
    The University of Auckland Library

    A fishery characterisation and stock assessment have been undertaken and accepted for SCI 3. A three stock model was developed, based on previous studies. Models excluding trawl or photo surveys were examined. Both approaches suggest SSB is currently around 54???60% SSB0. Models excluding trawl surveys suggest stock status would improve to 70% SSB0 by 2020 with future catches at the TACC, while models excluding the photo survey stock status would decline to 42% SSB0

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  • Estimating the abundance of scampi in SCI 6A (Auckland Islands) in 2016

    Tuck, Ian; Parkinson, D; Armiger, H; Smith, M; Miller, A; Rush, N; Spong, K (2017-01)

    Report
    The University of Auckland Library

    Photographic and trawl surveys of scampi in SCI 6A were conducted in February/March 2016. The photographic survey estimates of scampi and burrows both showed an increase on the 2013 estimate. The trawl survey estimate reflects a marked reduction from 2013, but an enforced vessel change raised questions over comparability with the previous series. Almost 3900 scampi were tagged and released to investigate growth and some animals have been recaptured by industry.

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  • Acute Respiratory Tract Infections and Vitamin D: Neonatal vitamin D levels and acute respiratory tract infections in the first year of life

    Saraf, Rajneeta (2016)

    Doctoral thesis
    The University of Auckland Library

    Background There is growing interest in vitamin D as an immune modulator and the role of vitamin D in respiratory illnesses is increasingly being recognised. Respiratory tract infections are a prevalent cause of hospital admission in the preschool-aged population; particularly in the first year of life. In order to try to reduce the ARI disease burden, it is necessary to understand the contribution of different risk factors acting at different phases of a child???s life. One risk factor that is of particular interest for this thesis is vitamin D status at birth. Aim My aim was to investigate the association between 25-hydroxyvitamin D (25[OH]D) status at birth and hospital admission with an acute respiratory tract infection in the first year of life. Two validation studies were also undertaken that allowed us to develop a dried blood spot liquid chromatography tandem mass spectrometry assay in a NZ laboratory and determine whether the developed assay was robust enough to measure 25(OH)D concentrations on dried blood spot samples stored for more than 5 years. Methods I performed a case-control study nested within Growing Up in New Zealand; a longitudinal study that is following 6853 children since their birth in 2009-2010. All the Growing Up in New Zealand cohort children hospitalised due to acute respiratory tract infections (ARI) in their first year of life were identified from linkage to the national collection of hospital events (the national minimum dataset (NMDS)). As part of the National Newborn Screening programme, 4 drops of blood were collected onto absorbent cards called dried blood spot cards (DBS). The DBS samples of respiratory cases (children in the cohort admitted with an ARI) and controls (cohort children matched with date of birth ?? 7 days and not hospitalised with an ARI) were tested for 25(OH)D concentration. Data collected during the antenatal period, birth and during infancy (9 months and immunisation register) were used to identify predictors of ARI in the first year of life. The dried blood spot 25(OH)D concentrations were categorised as deficient (3 people/bedroom (OR=1.84 95% CI 1.08 - 3.17) , living in a damp house (OR=1.54 95% CI 0.83 - 2.89), sleeping in rooms with heavy condensation (OR=1.80 95% CI 1.10 - 2.97), did not receive immunisations on time (OR=1.43 95% CI 0.89 - 2.27), and who spent on average <50 nmol/L) are twice as likely as children who are vitamin D sufficient at birth to be hospitalised with an ARI during infancy. Prevention of vitamin D deficiency during pregnancy and infancy has the potential to reduce the burden of severe ARI during infancy.

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  • What happens at work goes home: Investigating secondary traumatic stress and social support among the partners of New Zealand's Police, Fire, Ambulance and Defence Personnel

    Alrutz, Anna Stowe (2017)

    Doctoral thesis
    The University of Auckland Library

    Police, fire, ambulance and defence force personnel (responders) risk experiencing dangerous activities, traumatic events and the development of post-traumatic stress disorder. In turn, spouses/partners (partners) of these responders risk developing secondary traumatic stress (STS) as they are exposed vicariously to the trauma through communication with their responders. The research aimed to address the question: How do the partners of NZ defence and emergency responders respond to work stress experienced by their responder? The study used six research questions and six hypotheses to identify resources and barriers towards effective management of STS. A mixed methods approach assessed the experience of STS among the partners of New Zealand???s (NZ) responders. Using this approach the researchers interviewed participants prior to survey data collection and again after the survey to facilitate interpretation and incorporate feedback. After pilot-testing, the anonymous online survey was made available nationwide. The survey measured STS in partners, perceived stigma towards help-seeking, partner resilience and relationship satisfaction. The survey asked if the defence and emergency responder???s organisation invited partners to events, offered inductions, or offered informational resources to manage stress. Partners were asked who they turned to when dealing with stressful situations experienced by their responder. The survey concluded with open-ended questions about organisational engagement with the partners and responders. Themes were identified from analysis of the qualitative responses given by the 835 partners of NZ responders. A hypothesised model was produced and tested using multiple regression (n=664) which led to the creation of a structural equation model (SEM) (n=547) to describe interactions between resources and barriers. The study found that 20???35% of partners experience significant symptoms of STS and almost half feel unsupported when managing stressful issues experienced by their responders. Positive organisational communication benefits partners and reduces psychosocial risks. The thematic analyses endorsed increasing partner self-efficacy and encourages organisations to identify partner accessible resources. Triangulating the results obtained from these mixed methods highlights challenges faced by partners of defence and emergency responders and suggest how direct organisational engagement with the partners of their employees could reduce risks associated with secondary exposure to trauma.

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  • Gendered Academic Careers: A Comparison of Indonesia and New Zealand

    Toyibah, Dzuriyatun (2017)

    Doctoral thesis
    The University of Auckland Library

    This thesis aims to describe and better understand the gender gap in academic careers in Jakarta (Indonesia) and Auckland (New Zealand). The thesis is intended to measure and explain the operation of the gender gap, while also interrogating the construction of such indices as essentially Western in their assumptions. For example, The Global Gender Gap Report (World Economic Forum, 2015), rates New Zealand 10/145 and Indonesia, 92/145 of countries surveyed. A review of the global rankings shows a patterning of Western and non-Western countries and clearly invites deficit-based explanations in terms of development, culture, religion. As an Indonesian woman, such patterning also invites unease and disquiet. While I have experienced the everyday processes that produce the gender gap in academia and societally, I am also aware of the complexities and countervailing elements that reports like The Global Gender Gap Report might miss. One result of unease with a simple notion of the gender gap index, is to enrich research through the use of mixed methods, combining qualitative and quantitative approaches. This thesis explores and contextualises issues around the gender gap in academic careers, by using mixed methods across institutional cases based in Jakarta and Auckland. The methods used include: (i) secondary research, including analysis of promotion policies; (ii) an autoethnographic account, in which I discuss issues of gender, marriage, religion, patriarchy, motherhood, class, and social status; (iii) a quantitative analysis of differing datasets drawn from Indonesian and New Zealand institutions, using descriptive statistics, binary and ordinal regression; (iv) the non-comparability of datasets and of quantitative analysis reinforced my decision to include qualitative approaches in the mix of methods. Accordingly, I interviewed 30 academics in Auckland and Jakarta. The main findings of the research are: (i) It confirms the literature that male domination in academia is hidden and female academics who are mothers are marginalised. For academics who are also mothers, there is a collective understanding that the barriers are significant; (ii) Racial discrimination exists, but is largely invisible. Participants of colour acknowledged it and indeed had experienced it, though other participants, in the same universities, believed that it no longer occurred. Arguably, gender and race are rendered invisible in academic careers under a neo-liberal system, especially when using statistical analysis, as such elements are considered non-meritocratic factors; (iii) Understanding the academic gender gap in Indonesia is better framed by considering the fact that career progression follows civil servant regulation, and is not perceived as very prestigious in terms of income. Rather, being an academic, according to some Indonesian academics, is about a ???calling??? and devotion to knowledge development; (iv) On the other hand, studies in liberal, Western countries emphasise that family life, children, and domestic work are serious problems for female academics. To be single or childfree is considered to enhancefemale academic careeradvancement. In conclusion, comparing the scale of the gender gap index between liberal countries such as New Zealand and non-liberal countries such as Indonesia is very challenging due to cultural and structural differences. My research underscores that it is important to measure women???s conditions beside indicators developed in the Gender Gap Index (economic participation and opportunity, educational attainment, health and survival and political empowerment). It is necessary to include indicators which are accepted in all cultures and nations, such as the index of happiness, life satisfaction; indicators must align with desires and hopes for the future. Critique is essential to create the conditions for transformative change but that change should align with individual and collective aspirations.

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  • Examining the Roles of Residuals Under an Adaptation Level Theory Model for Tinnitus Perception

    Durai, M (2016)

    Doctoral thesis
    The University of Auckland Library

    Background: Tinnitus is the perception of sound in the absence of sound in the environment (1-4). The precise mechanisms giving rise to tinnitus perception and distress are still not fully known. The Adaptation Level Theory (ALT) model of tinnitus (5, 6) is an ecological framework which takes a holistic approach to understanding tinnitus and its complexity, in which tinnitus magnitude estimates are based on interactions between the focal component (tinnitus), contextual component (any background noise or applied sounds), and residual components (individual cognitive and behavioural characteristics). Aim: To empirically explore the influence and strength of individual residual factors under a novel Adaptation Level Theory (ALT) model of tinnitus perception. Personality traits, emotion and prediction/anticipation of sounds were residuals examined. Methods: Seven studies were undertaken as part of this doctoral thesis: 1) A scoping review investigated key personality traits relevant to tinnitus, and the relationship between affective disorders and tinnitus. 2) A web-based survey was administered to 154 individuals with tinnitus and 61 age, gender and hearing level-matched non-tinnitus controls. The survey measured four key self-reported personality traits (social closeness, stress reaction, alienation and self-control), tinnitus characteristics and hearing handicap. 3) A behavioural experiment (N=22) introduced short-term emotional stimuli, differing along valence and arousal dimensions, and measured tinnitus loudness and annoyance characteristics. Stimuli were presented in two modalities: auditory and visual. 4) A comprehensive narrative synthesis of current research assessed the feasibility of a relationship between auditory memory, predictive coding and tinnitus generation. 5) A short-term adaptation experiment (N=23) and two-week feasibility trial (N=7) compared the effect of predictable and unpredictable amplitude-modulated computer surf sound on tinnitus loudness and annoyance characteristics. 6) An electroencephalography (EEG) study that compared mean ERP amplitudes and oscillatory band activity in response to tone deviants and tone omissions (at the pitch of tinnitus) between individuals with tinnitus (N=16) and hearing-level matched controls (N=14). 7) A randomized tinnitus sound therapy clinical trial (N=18) was conducted comparing the effectiveness of nature sounds with neutral broadband noise. Multiple experimental outcomes relating to tinnitus, emotion, attention and psychological state were measured at three time points: at sound fitting, 4 weeks after administration and 8 weeks after administration. Results: 1) The scoping review concluded personality traits to have a consistent association with the distress experienced by adult tinnitus help-seekers, and help-seekers were also more likely to experience anxiety and depression symptoms and/or disorders. Limitations present in current research were lack of appropriately controlled comparisons when assessing personality trait profiles of tinnitus sufferers and non-tinnitus individuals. 2) Tinnitus sufferers displayed higher levels of stress reaction, lower social closeness, lower self-control and higher alienation than the control group in the web-based survey. 3) In the behavioural emotion experiment, low valence (unpleasant) auditory stimuli led to higher subjective tinnitus loudness ratings in males and females and higher subjective distress ratings in males only. Visual emotional stimuli did not have an effect on tinnitus characteristics. 4) The narrative review provided theoretical support and indirect electrophysiological evidence for continuous prediction errors generated within the auditory system driving tinnitus perception and distress, as well as eliciting global disruptions to attention and working memory. 5) Both short-term Unpredictable and Predictable sound administration led to a decrease in tinnitus loudness in the adaptation experiment, however, only Unpredictable sound lowered tinnitus distress ratings. 6) A larger N1c waveform was elicited in the absence of any tone deviation within the left primary auditory cortex of tinnitus participants for the EEG study. Abnormal N1c waveform growth was present across levels of deviant conditions for the tinnitus group. There was limited evidence to support the Thalamocortical Dysrhythmia hypothesis of greater theta and gamma activity present among individuals with tinnitus. A role for attention and auditory scene analysis in driving tinnitus perception and salience was supported. No differences were present between groups for tone omissions. Different levels of activity between tinnitus and control groups were observed in regions corresponding to attentional as well as limbic networks. 7) The administration of sound therapy led to significant reduction in tinnitus impact over 8 weeks; this effect was largely due to BBN sound therapy which resulted in significantly greater reduction of tinnitus impact compared to nature sounds. The positive effect of sound on tinnitus was supported by secondary tinnitus and psychologicalrelated outcome measures, but not interviews. BBN sound resulted in an increase in loudness level matches needed to match tinnitus; there was minimal change in loudness level matches for nature sounds. There were indications of individual preferences and individual outcome effects observed. The presence of tinnitus subgroups was apparent in terms of which sound was most favoured, which sound had the most benefit, as well as in how sound-tinnitus interactions occurred as time progressed. Conclusions: Personality traits, emotion and prediction all play a significant role as residual factors under the ALT model to shape final tinnitus perception and experience as well as in influencing response of tinnitus to introduction of external sound introduction. Overall, tinnitus magnitude appears to increase with high stress reaction, low social closeness, low self-control and high alienation personality trait levels, as well as by the introduction of unpleasant auditory stimuli. In contrast, the presence of sound therapy stimuli decreases tinnitus magnitude and demonstrates psychological benefit over time. This thesis provides some empirical support for the ALT model of tinnitus. Further research is needed to examine attention as a weighting factor, develop clinically useful indicators of ideal sound therapy levels under the ALT framework, as well as customize therapeutic sound to tailor for individual residual levels, needs and preferences over time. Development of computational models based on the ALT which integrate residual factors, weighting factors and tinnitusexternal sound interactions may be useful for delineating subgroups and predicting how an individual might respond to potential treatments. The findings from this thesis can form a basic computational template to build-on.

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  • When to Start, What to Start and Other Treatment Controversies in Pediatric HIV Infection

    Turkova, A; Webb, Rachel; Lyall, H (2012-12)

    Journal article
    The University of Auckland Library

    Over the last decade there have been dramatic changes in the management of pediatric HIV infection. Whilst observational studies and several randomized control trials (RCTs) have addressed some questions about when to start antiretroviral therapy (ART) in children and what antiretrovirals to start, many others remain unanswered. In infants, early initiation of ART greatly reduces mortality and disease progression. Treatment guidelines now recommend ART in all infants younger than 1 or 2 years of age depending on geographical setting. In children >1 year of age, US, European (Paediatric European Network for Treatment of AIDS; PENTA) and WHO guidelines differ and debate is ongoing. Recent data from an RCT in Thailand in children with moderate immune suppression indicate that it is safe to monitor asymptomatic children closely without initiating ART, although earlier treatment was associated with improved growth. Untreated HIV progression in children aged over 5 years is similar to that in adults, and traditionally adult treatment thresholds are applied. Recent adult observational and modeling studies showed a survival advantage and reduction of age-associated complications with early treatment. The current US guidelines have lowered CD4+ cell count thresholds for ART initiation for children aged >5 years to 500 cells/mm3. Co-infections influence the choice of drugs and the timing of starting ART. Drug interactions, overlapping toxicities and adherence problems secondary to increased pill burden are important issues. Rapid changes in the pharmacokinetics of antiretrovirals in the first years of life, limited pharmacokinetic data in children and genetic variation in metabolism of many antiretrovirals make correct dosing difficult. Adherence should always be addressed prior to starting ART or switching regimens. The initial ART regimen depends on previous exposure, including perinatal administration for prevention of mother to child transmission (PMTCT), adherence, co-infections, drug availability and licensing. A European cohort study in infants indicated that treatment with four drugs produced superior virologic suppression and immune recovery. Protease inhibitor (PI)-based ART has the advantage of a high barrier to viral resistance. A recent RCT conducted in several African countries showed PI-based ART to be advantageous in children aged <3 years compared with nevirapine-based ART irrespective of previous nevirapine exposure. Another trial in older children from resource rich settings showed both regimens were equally effective. Treatment interruption remains a controversial issue in children, but one study in Europe demonstrated no short-term detrimental effects. ART in children is a rapidly evolving area with many new antiretrovirals being developed and undergoing trials. The aim of ART has shifted from avoiding mortality and morbidity to achieving a normal life expectancy and quality of life, minimizing toxicities and preventing early cancers and age-related illnesses.

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  • Review of: Conny Kristel, De Oorlog van Anderen. Nederlanders en Oorlogsgeweld, 1914 - 1918. Amsterdam, De Bezige Bij, 2016

    Abbenhuis, Maartje (2017-03)

    Journal article
    The University of Auckland Library

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  • Prevalence of Rheumatic Heart Disease and Other Echocardiographic Abnormalities in Polynesian Young Adults in South Auckland, New Zealand

    Webb, Rachel; Culliford-Semmens, N; Mow, AC; Doughty, R; Tilton, E; Peat, B; Stirling, J; Gentles, T; Stewart, J; Wilson, N (2016-06)

    Conference item
    The University of Auckland Library

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  • Long-Term Outcomes of New Zealand Children and Young Adults Undergoing Surgery for Rheumatic Heart Disease

    Webb, Rachel; Remenyi, B; Finucane, K; Lennon, D; Gentles, T; Sidhu, K; Wilson, N (2016-06)

    Conference item
    The University of Auckland Library

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  • Sequential Intravenous High Dose Oral Antibiotics in the Treatment of Osteoarticular Infections in Children: A Randomized Controlled Trial

    Tsui, K; Crawford, H; Mow, FC; Webb, Rachel; Voss, LM; Stott, NS; Stewart, J; Lennon, DR (2016)

    Conference item
    The University of Auckland Library

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  • The Microbiology of Septic Arthritis in Young Auckland Children

    Boom, MVD; Webb, Rachel; Lennon, DR; Crawford, H; Freeman, J; Castle, J; Mistry, R (2016-12-01)

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    The University of Auckland Library

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  • Development of novel nanoparticulate delivery system for oral delivery of gemcitabine to treat breast cancer

    Chen, Guanyu (2016)

    Doctoral thesis
    The University of Auckland Library

    Background and Aim: In New Zealand women, breast cancer has a highest rate of incidence of any cancer. In 2015, there were approximate 60,300 new cases of breast cancer diagnosed globally, which is second most common cancer overall. To address breast cancer, chemotherapy is typically administered parenterally. However, this is an unpleasant and inconvenient administration route, and often leads to high peak levels of drug in the systemic circulation above the maximum tolerated concentration (MTC) resulting in a multitude of side effects. Oral chemotherapy is attractive with better patient acceptability, good therapeutic efficacy, and low cost. However, there are many obstacles to achieve oral drug delivery including physical and biochemical barriers, such as the epithelial barrier of the small intestine, degradation through the acidic environment of the stomach and digestive enzymes throughout the gastrointestinal tract, as well as efflux pumps which limit oral drug absorption. Gemcitabine is a promising drug candidate with proven activity against breast cancer, however, it has an oral bioavailability of less than 10%, due to its high hydrophilicity and low permeability through intestinal epithelium. Therefore, the aim of this project was to develop a novel nanoparticulate drug delivery system for oral delivery of gemcitabine, to improve its oral bioavailability. Methods: Two different polymeric nanoparticulate delivery systems were designed suitable for the oral delivery of gemcitabine. The first was gemcitabine-loaded TMC modified PLGATPGS nanoparticles (NPs) prepared through a modified solvent evaporation technique. The PLGA-TPGS random copolymer was synthesized prior to the fabrication of NPs. A central composite design (CCD) was applied to optimize the formulation parameters. The second delivery system of gemcitabine loaded TMC-CSK NP was fabricated via an ionic gelation method. The TMC polymer was synthesized by using a new two-step methylation method prior to preparing the TMC based NPs. The physical and chemical properties of both nanoparticulate delivery systems were determined including particles size, zeta potential, entrapment efficiency, in-vitro drug release and ex-vivo drug permeation over the porcine epithelial membrane, and the optimal formulations were selected. A co-cultured Caco-2 and HT29-MTX-E12 cell model was set up to determine cytotoxicity, cellular uptake and transport studies of the drug solution and optimal drug loaded NPs. Finally, the pharmacokinetic parameters associated with different formulation were determined using a Sprague-Dawley (SD) rat model. The tumour growth rate associated with the drug solution and the drug loaded NPs were investigated using a BALB/c nude mouse model. Results and discussion: The optimal formulations of drug loaded TMC modified PLGATPGS NPs and drug loaded TMC-CSK NPs showed particle size of 243.21 ?? 21.72 nm, and 173.60 ?? 6.82 nm, zeta potential of +14.70 ?? 1.31 mV, and +18.50 ?? 0.22 mV, entrapment efficiency of 76.43 ?? 0.21%, and 66.43 ?? 0.13%, respectively. Particles of less than 500 nm show significantly higher absorption than larger particles across intestinal epithelium, thus the particle sizes of both NPs are suitable for oral absorption. NPs with zeta potentials more positive than +15 mV or more negative than -15 mV are considered stable, thus the two NPs are considered having good steric stability. In addition, the positive charged NPs promote mucoadhesion with the negatively charged intestinal mucosa, through electrostatic interaction. The high entrapment efficiency results were promising and are higher than most polymeric NPs delivery systems reported. Scanning electron microscopy (SEM) showed the TMC modified PLGA-TPGS NPs were spherical with a smooth particle surface, while the TMC-CSK NPs had more irregular shape with a craggy particle surface. They both showed sustain drug release profiles during in vitro drug release studies, and greater drug permeation compared to drug solution over porcine epithelial membrane in the ex-vivo drug permeation studies. Moreover, both optimal drug loaded NPs exhibited good stability in terms of particle size and drug entrapment over 3 months stored at 4??C. The cytotoxicity of gemcitabine solution, gemcitabine loaded TMC modified PLGA-TPGS NPs, and gemcitabine loaded TMC-CSK NPs on Caco-2/HT29-MTX-E12 cells showed dose dependence and with IC50s of 529.4 ?? 67.2 ??g.mL-1, 1881.4 ?? 51.5 ??g.mL-1 and 1682.4 ?? 27.9 ??g.mL-1 respectively, indicating the drug loaded NPs were less toxic to the intestinal epithelial cells compared to the drug solution. The rate of cellular uptake of both optimal drug loaded NPs was time-, temperature-, and concentration- dependant. Cellular uptake for the gemcitabine loaded TMC modified PLGA-TPGS NPs undergo active transport involving adsorptive mediated endocytosis and caveloae mediated endocytosis, while the gemcitabine loaded TMC-CSK NPs was through active transport associate with adsorptive mediated, clathrin and caveolae mediated endocytosis. In cellular transport studies, both drug loaded NPs had greater drug transport capability compared to drug solution over the Caco-2/HT29- MTX-E12 cell membrane. For the transport mechanism studies, both NP formulations showed electrostatic interaction with the intestinal epithelial cells. P glycoprotein (P-gp) efflux affected the cellular transport for both NPs. By blocking the P-gp efflux pump, more drug loaded NPs were transported through the cell membrane. The multiple resistance protein-2 (MRP2) only affected TMC-CSK NPs to some extent. Interestingly, for the TMC modified PLGA-TPGS NPs, the addition of the MRP2 inhibitor resulted in a reduction in the efflux of gemcitabine suggesting that the role of MRP2 in the efflux of gemcitabine loaded TMC modified PLGA-TPGS NPs can be neglected. Moreover, EDTA is able to activate the cellular protein kinase C (PKC) by depletion of extracellular calcium via chelation, resulting in tight junction opening. The addition of EDTA significantly enhanced the cellular transport for both drug loaded NPs, facilitating the transport of the NPs via the paracellular route. In the in vivo pharmacokinetic studies, the half-life (t1/2) and oral bioavailability of gemcitabine were significantly improved in drug loaded NPs compared to drug solution group. The t1/2 of gemcitabine loaded TMC-CSK NPs and gemcitabine loaded TMC modified PLGA-TPGS NPs were of 77.16 ?? 24.20 hr and 69.98 ?? 20.50 hr, respectively, compared with 9.40 ?? 2.13 hr for the gemcitabine solution. The absolute oral bioavailability of gemcitabine loaded TMC-CSK NPs (55.20%), was 1.1-fold and 6.1-fold higher than that of gemcitabine loaded TMC modified PLGA-TPGS NPs (49.92%) and gemcitabine solution (9.86%), respectively. In pharmacodynamics studies, the drug loaded NPs had greater inhibition of tumour growth rate compared with the drug solution (p < 0.01). The gemcitabine loaded TMC-CSK NPs group had the greatest inhibition of tumour growth, with 3.12-fold and 1.78-fold reduction compared to saline control group and gemcitabine solution group, respectively. This result corresponds to the pharmacokinetic studies with greater oral bioavailability and longer plasma half-life of gemcitabine loaded TMC-CSK NPs group compared to all other groups. Conclusion: This project has demonstrated that TMC modified PLGA-TPGS NPs and TMCCSK NPs can be utilised as controlled release drug delivery systems for the oral delivery of gemcitabine. Encapsulated gemcitabine is able to overcome the physical and biochemical barriers in GIT, to enhance the drug absorption over the intestinal epithelial membrane, therefore improving the oral bioavailability of gemcitabine, and promoting the anticancer therapeutic efficacy. The promising results confirmed the two developed NPs are promising platforms for developing future oral chemotherapy products loaded with gemcitabine.

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