2,799 results for ResearchSpace@Auckland, Modify

  • Nonlinear Processes in Optical Fibers and Microresonators

    Webb, Karen

    Thesis
    The University of Auckland Library

    This Thesis presents a series of experimental and numerical investigations of nonlinear frequency conversion processes in both optical fibers and microresonators. In the context of optical fibers, we consider the cascaded four-wave mixing dynamics that underlie the interaction between solitons and linear waves, while in microresonators we look in detail at the formation of optical frequency combs and their properties. We first consider the interactions between solitons and weak linear waves co-propagating in an optical fiber. Through comprehensive experiments and simulations, we demonstrate the equivalence between soliton-linear wave interactions and cascaded Bragg scattering. The observed dynamics are also interpreted in terms of fiber-optic analogues of event horizons. We also investigate cascaded four-wave mixing processes in optical fibers in the absence of weak input linear waves. Specifically, we examine the excitation of a higher-order sideband that is phasematched through the cascade, and study how the efficiency of this excitation depends on the frequency detuning between the two continuous-wave pumps that initiate the four-wave mixing process. We find that the pump separation has a significant effect on the conversion efficiency to the phasematched sideband, which we explain by treating the individual cycles of the pump beat note as independent higher-order solitons. In the study of microresonators, we quantify the coherence properties of different microres-onator frequency combs. By passing the resonator output through a delayed interferometer, the modulus of the complex degree of first order coherence can be extracted from the spectral fringes. In addition to allowing for the quantitative assessment of comb coherence across the full bandwidth, we demonstrate how this method can be used to experimentally determine the comb operating regime. Finally, we demonstrate for the first time the formation of temporal cavity solitons in silica microspheres, and experimentally verify the high coherence of the resulting frequency combs. Further experiments and numerical simulations are carried out to investigate the influence of perturbations on the generation of microresonator cavity solitons.

    View record details
  • Calorimetry of an ultracold Bose gas and cavity quantum electrodynamics with an optical nanofibre

    Ruddell, Samuel

    Thesis
    The University of Auckland Library

    In this Thesis we present experiments involving laser cooled alkali atoms. We perform calorimetry experiments with a harmonically trapped Bose gas of 87Rb atoms. Starting from a Bose-Einstein condensate confined in an optical trap, we transfer a precise and known amount of energy to the system using one of two independent methods. Following a rethermalisation period within the trapping potential, we measure the resulting temperature of the atoms through absorption imaging. Comparisons of experimental data to various theoretical models show that the thermodynamic behaviour of the system is well described by a Hartree-Fock model for an interacting gas. In a separate experiment we have utilised a nanofibre, a section of optical fibre that has been tapered to a subwavelength diameter waist, as a tool for interfacing 133Cs atoms with the guided optical mode of the fibre through an evanescent field. The tight transverse confinement of the guided mode allows for efficient light???matter interactions at the few photon level. We enhance these interactions by forming an all-fibre ring geometry cavity containing a nanofibre section, and perform cavity quantum electrodynamics experiments with an ensemble of laser cooled caesium atoms. Due to a collective enhancement of the coupling rate by the ensemble of atoms, we observe well-resolved vacuum Rabi splitting of the cavity transmission in the weak driving limit. Additionally, we investigate the power dependence of the atom???cavity transmission on resonance, and observe saturation of the atoms at higher driving strengths. We also present a simple theoretical model to describe the behaviour of this system. Finally, modern cold atom experiments demand a high degree of control and reproducibility, which can be best provided through computer control. We present our implementation of a computer interface for the experiment, as well as various custom built hardware interfaces which are integrated into our control scheme. Our system allows for scripting of an experimental sequence, adjustment of experimental settings, and the ability to collect and analyse experimental data from a central computer.

    View record details
  • Assessing the effects of brief stimuli unrelated to reinforcement

    Bai, John

    Thesis
    The University of Auckland Library

    Reinforcers are environmental events defined by their effects on behavior. However, brief, arbitrary stimuli can also have reinforcement-like effects, despite being unrelated to food reinforcement. The present thesis explored the potential reinforcement-like effects of brief stimuli across five experiments. In Experiments 1 through 4, pigeon subjects responded for food reinforcement and brief stimulus presentations in a two-component multiple schedule. Neither baseline response rates nor resistance to change during disruption tests were systematically greater in a component with versus without brief stimulus presentations. Additionally, increasing the rate and duration of brief stimulus presentations in Experiment 4 failed to reveal reinforcement-like effects when compared directly with food. In Experiment 5, pigeons chose between independent terminal links in a concurrent-chains procedure. Across conditions, varying the location, duration, and rate of brief stimulus presentations in the terminal links had no systematic effects on preference. In contrast, varying rates of food reinforcers resulted in large and reliable shifts in preference. Therefore, the present thesis did not find any evidence that brief stimuli unrelated to food reliably increase response rates, resistance to change, or preference. These data demonstrate the value of systematic replication, and a behavioral momentum approach to assessing potential reinforcement-like effects.

    View record details
  • Majority Influence in Infancy

    Anantharaman, Sweta (2017)

    Doctoral thesis
    The University of Auckland Library

    Majority influence is an integral aspect of many human societies; it is an important catalyst of learning and promotes transmission of cultural knowledge. Given the importance that majorities play in human societies, it is not surprising that young children are sensitive to information gleaned from majorities. A growing body of evidence raises the interesting, yet unexplored possibility that, like preschool-aged children and adults, infants??? behaviour might be influenced by majorities. Using a novel eye-tracking paradigm, the experiments reported across the three manuscripts examined the characteristics of, and extent to which, majorities bias infants??? behaviour in different contexts, primarily via visual attention. Chapter 2 examined whether a majority influenced 18-month-old infants' preference (i.e., looking time and behavioural preference) for two novel toys. The results across two experiments revealed that infants' visual preference for a novel toy was not influenced by the majority if they were first provided with experience with the toys, but was marginally influenced if infants received no prior experience with the toys. These experiments provided useful insights into the role that context and social cues play in guiding infants' attention. By introducing an element of ambiguity (using boxes rather than novel toys) and adding cues to boost majority salience, Chapter 3 examined whether 12- and 19-month-old infants' attention to a novel stimulus was influenced by the majority. The findings across two experiments provided the first known evidence that infants??? attention is guided by majority information at 19-, but not at 12-months of age. Further, the results indicated that infants??? attention was guided by a majority only when all majority members are shown to prefer one object to another. Finally, Chapter 4 examined the role of novel social categories and social affiliation in guiding 19- and 24-month-old infants' expectations of group members and further, whether infants' attention for novel stimuli would be biased by these expectations. The results indicated no influence on infants' attention to novel stimuli based on social categories or social affiliation across both age groups. However, looking time patterns towards events leading up to the test phase among 24-month-old infants indicated interesting trends in their understanding of groups as cohesive units. Together, the findings across the three manuscripts offer preliminary evidence of majority influence as well as the role of social cues in infants' expectations of group cohesiveness in driving visual attention early in development. Crucially, these findings suggest, to our knowledge, the first known evidence of majority bias at 19-months. Infants??? sensitivity towards the majority at the visual attention level is the likely foundation for subsequent selectivity to majority information across domains.

    View record details
  • Approaches to Describe and Quantify Uncertainty in Bio-physical Agricultural Computer Simulation Models

    Meenken, Esther (2016)

    Doctoral thesis
    The University of Auckland Library

    The objective was to explore the definition, sources, quantification, and management of uncertainty in bio-physical agricultural deterministic computer simulation models (crop models). One aim was to provide recommendations from a formalised statistical viewpoint on management of uncertainty for a small pool of crop model researchers in New Zealand. These researchers face unique issues with models that describe temperate, island-based conditions. An equally important goal was to identify ways to provide predictions complete with uncertainty bounds beyond those offered by sensitivity analysis. Given these objectives, my focus was on a single model. Section I proposes an uncertainty evaluation (UE) framework to explore how the combined components of a crop model contribute to the overall output uncertainty. Tools to curate information, diagnose the most important sources of uncertainty, and identify UE objectives have been developed. The framework links qualitative and quantitative analysis through a review of techniques for generating and analysing data from such models. Although many elements considered appear in the literature, amalgamation into a united framework is an original contribution. In Section II a detailed description of a case-study model that simulates wheat development is provided. This model provides a concrete foundation by which to demonstrate the UE framework, and illustrates the nature of crop models as constructs upon which mechanistic understanding of real-world systems continues to develop. A theoretical addition to a recent model that combines physiological and genetic characteristics of wheat is proposed based on laboratory based experimental work, reducing structural uncertainty. Finally, Section III is centred on the analysis of simulated data. In particular, it addressed the desire to provide credible intervals for state-space model estimates. This was achieved through fitting a probabilistic Bayesian hierarchical model with MCMC, a general form of data assimilation that recursively updates state predictions based on available data. Credible bounds of both an observed and a latent state variable were estimated for the case-study model. Finally, I summarise how these three sections tie together to resolve research objectives. I discuss the benefits of this research, recommendations and limitations, and propose directions for future work.

    View record details
  • 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.

    View record details
  • Women Godfathers of Organised Crime: As Presented by Twenty-Three Auto/Biographies

    Tregunna, Alice (2017)

    Doctoral thesis
    The University of Auckland Library

    This thesis is guided by a grounded theoretical framework and explores the experiences presented in the auto/biographical accounts of women who have occupied management positions in illicit businesses and organised criminal networks. This project brings attention to a previously under-researched phenomenon within criminological research: the role of women as perpetrators within organised crime and not only as victims. It highlights that the current conceptualisation of organised crime as a ???male??? business is incorrect. The findings of this project demonstrate that women have occupied controlling positions for at least 150 years, across various countries and industries, and that similarities can be identified in their illicit career pathways. A narrative analysis is conducted of women's criminal career pathways in illicit business. Consideration is given to social and political factors impacting their entrance into an illicit industry and the complex process of patriarchal bargaining taking place once they have become active in organised criminal behaviours. A commonality between the women???s social position, specifically their corresponding levels of social, cultural and economic capital, and the illicit industry they initially participated in was identified. Furthermore, their reliance on gatekeepers to facilitate entrance into an illicit business and their succession within family businesses during times of crisis is discussed. This leads onto consideration of the push and pull factors experienced by the women, because of legislation and policy changes. An examination of women's experiences of abuse and utilisation of violence is conducted to produce a new theoretical model of women's criminal career pathways in organised crime. This considers the business strategies of sex and violence utilised by the women, in conjunction with their reliance on neutralisation techniques to rationalise their illicit business activities, allowing for their continued involvement in organised criminal activities. Overall, this research highlights the complex processes undertaken by women to achieve leadership positions within organised criminal networks and illicit business. The thesis contributes to criminological knowledge about women???s involvement in organised crime and the literature on gender and crime more broadly, through the analysis of the representations of women???s pathways through illicit business and organised criminal networks.

    View record details
  • Practical Output Regulation of Non-Minimum Phase Nonlinear Systems

    Postelnik, Leron (2016)

    Doctoral thesis
    The University of Auckland Library

    This thesis focuses on the output regulation of control-affine time-invariant non-minimum phase nonlinear systems, specifically regarding the output tracking of time-varying signals in the presence of system uncertainty. Much of the published output regulation theory for this class of system faces significant barriers to practical application. The more practical approaches, which are not limited by these same barriers, have seen limited application to practical systems within the literature. Three such approaches ??? the kth-order approximate output regulator, the kth-order robust output regulator, and the stable system centre based sliding mode control approach ??? are herein applied to two case studies in order to both provide additional examples of their application to physically meaningful systems and to gain further insight into the strengths and weaknesses of each approach in regard to practical application e.g. when facing various forms of system uncertainty. Furthermore, a novel "approximate stable system centre" approach was developed and shown to provide improved tracking performance over the standard stable system centre approach under certain conditions. The two case studies considered are the spherical inverted pendulum, which is a more complex system compared to the standard SISO inverted pendulum on a cart commonly used a benchmark nonlinear system, and the two-wheeled balancing robot, which serves as a direct practical application in the area of mobile robotics. Simulations were conducted for the 2D position control of the spherical inverted pendulum and the 2D forward and yaw speed control of the two-wheeled robot in the presence of parametric and unstructured uncertainty. Measurement noise and delay was additionally considered in the two-wheeled robot simulations. Experimental testing was also conducted for the straight-line position control of the two-wheeled robot. Overall, the kth-order robust output regulator provided the most accurate steady state tracking under most conditions considered, but suffered from poor transient response. The kth-order approximate output regulator gave the fastest transient response, but only provided acceptable steady state performance under low levels of uncertainty. The approximate stable system centre approach provided a well-balanced performance under most conditions, but was the most sensitive to the presence of system delays due to use of the sliding mode controller.

    View record details
  • The Impact of a Medical Curriculum on Motivation and Well-being Among Medical Students

    Lyndon, Mataroria (2016)

    Doctoral thesis
    The University of Auckland Library

    Aim The aim of this thesis was to determine the impact of critical aspects of a medical curriculum on motivation and well-being, and how these constructs affect academic achievement among medical students. Method A multi-methods approach incorporating systematic review and quantitative and qualitative studies was undertaken. More specifically, this approach included reviewing the literature of motivation and well-being among medical students; exploring motivation and well-being by year level of a curriculum and admissions criteria (qualitative study); evaluating the effect of a medical curriculum on motivation and well-being over time (longitudinal study); examining motivation and well-being among ethnic groups (cross-sectional study); evaluating a change of medical curriculum on motivation and well-being (cross-sectional comparative study); and investigating associations between motivation, well-being and academic achievement (person-oriented approach). Results The systematic review found valuable associations between the constructs of motivation and well-being that were moderated by demographic and curriculum variables. Furthermore, it indicated a relationship may exist between motivation, well-being and academic achievement. The qualitative study found clear differences in student expression between admissions criteria and year level, suggesting that the curriculum and sociocultural influences are mediators of motivation and wellbeing. Furthermore, changes in motivation and well-being occur longitudinally, which differ by year level of the curriculum and admissions criteria. The cross-sectional study found differences in motivation and well-being among indigenous and ethnic minority medical students. The comparative cohort study found no significant differences in motivation and well-being between cohorts of medical students under traditional and revised curricula; however, differences were found among students in their clinical years of training. Finally, associations between motivation and wellbeing were observed, which had a relationship with academic achievement over time. Conclusion A medical curriculum has an impact on motivation and well-being, which differs by year level, admissions criteria, and ethnicity. Furthermore, a relationship exists between motivation and well-being, and academic achievement. These findings have implications for student recruitment and retention, student equity and curriculum development, and highlights the challenges of facilitating learning environments and curricula that support optimal forms of motivation and enhance well-being for all students.

    View record details
  • Regulatory and Non-Regulatory Influential Factors for Earnings Management by Real Estate Investment Trusts

    Liang, Jian (2016)

    Doctoral thesis
    The University of Auckland Library

    This research investigates how non-regulatory, and regulatory factors influence the Earnings Management (EM) by Real Estate Investment Trusts (REITs). The regulatory factors pertain to the REITs??? regulatory regimes. The non-regulatory factors include the composition of property portfolios, the choice of the security structure, the 2007 global financial crises (GFC), EM persistence and the trade-off between different EM measurements. This study is based on quantitative methodology, and it uses an unbalanced panel database with information of REITs from major REIT markets from 2000 to 2013. This research extends and modifies models from existing literature to estimate the EM measurements of REITs. Static and dynamic panel data models are used in empirical tests. Treatment effect estimators are employed to analyse the impact of security structure choice and REITs??? conversion on EM. This research provides the following findings: (1) The variances of the proportions of different types of property in the property portfolio held by New Zealand Listed property portfolios have a significant impact on the magnitudes of using various EM approaches. (2) The 2007 GFC has changed the EM behaviour of the U.S equity REITs. (3) Compared to unstapled Australian REITs, stapled Australian REITs engage in EM activities in a greater magnitude. (4) The measurements of EM activities in the current accounting period react to their own value in the previous accounting period and the measurements of other EM activities in the previous accounting period in different manners. (5) Listed real estate corporations change their EM behaviour to prepare for their REIT conversion. Listed real estate corporations are different from REITs in regard to their EM behaviour. (6) The magnitudes of accrual EM activities are found to be positively correlated with the abnormal volatilities of the leverage ratio and the dividend pay-out ratio. (7) The incentive for REITs to comply with the requirements for leverage ratio and dividend pay-out ratio significantly impacts the magnitudes of EM measurement. These results contribute to the understanding of information asymmetry, efficient market hypothesis and corporate governance in the context of REITs. The findings enhance investors??? and policymakers??? knowledge of the disclosure of financial information for REITs and may assist in improving transparency in REIT markets.

    View record details
  • Robust Control of Nonlinear Systems: Sliding mode and Non-monotonic Approaches

    Nasiri Minab, Alireza (2016)

    Doctoral thesis
    The University of Auckland Library

    The field of robust controller design for nonlinear systems has been an important area of research in the control community over the past few decades. Lyapunov based control design methods have developed into an established class of procedures for robust control design. This dissertation initially applies the standard Lyapunov function approach to design an adaptive sliding mode controller (SMC). Next, the non-monotonic Lyapunov approach, which is a variant of the classical Lyapunov approach, is utilised to design a robust controller for discrete-time nonlinear systems represented by a Takagi-Sugeno (T-S) fuzzy model. An adaptive scheme of designing SMC for the affine class of multiple input multiple output (MIMO) nonlinear systems with norm bounded uncertainties is proposed during the first stage of the research. The proposed adaptive SMC does not require a priori knowledge of the bounds of uncertainties and therefore offers significant advantages over non-adaptive schemes of SMC design. Next, this controller is developed to be fault tolerant for actuator faults. The actuator fault is represented by a multiplicative factor of the control signal which reflects the loss of actuator effectiveness. The design of the controller is based on the assumption that the maximum loss level of actuator effectiveness is known. The effectiveness of the proposed controllers is demonstrated considering a two-link robot manipulator. The stability analysis and stabilisation of discrete-time nonlinear systems described by T-S fuzzy models are investigated and new design procedures are proposed in the second stage of this thesis. The stability analysis of T-S fuzzy models and subsequently the controller design are often carried out through the Lyapunov method. This leads to some inherent inequalities in which the nonlinear membership functions are excluded from the final analysis and synthesis conditions. As a result the stability conditions, which are often constructed in the form of linear matrix inequalities (LMIs), become only sufficient (conservative). To reduce this conservatism, the assumption of monotonic decrease of Lyapunov function has been relaxed giving a new approach to the control design known as the non-monotonic Lyapunov approach, where the Lyapunov function is no longer required to decrease in each successive time step (i.e., Vt+1 < Vt ). Instead, small local growth is allowed but ultimately it converges to zero. In recent years, various researchers have used the k-samples variations approach (i.e., Vt+k

    View record details
  • 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.

    View record details
  • Characterisation of a protease-dependent gene regulation system for gene therapy applications

    Naidoo, Jerusha (2015)

    Doctoral thesis
    The University of Auckland Library

    Gene therapy is a promising approach for the treatment of a wide range of chronic diseases. These therapies typically utilise strong, constitutively active promoters to drive high levels of recombinant protein expression. Unregulated gene expression is a key issue limiting clinical translation of promising gene therapies due to the potential for side-effects from excessive levels of protein that indiscriminately affect both diseased and non-diseased cells. Ideally gene expression would be regulated such that it would be quiescent under basal conditions and induced to a therapeutic level in at-risk cells only. This thesis describes the characterisation of a novel bicistronic autoregulatory gene expression system that relies on cell stress-induced activation of specific proteases to drive transgene expression. The functionality of this system was assessed in vitro in a model of cellular stress and in vivo in a neurotoxin model of Parkinson???s disease, a neurodegenerative disorder associated with aberrant activation of the specific proteases caspase-3 and calpain. The results showed that transgene expression under control of the gene regulation system was low under basal conditions and inducible in a concentration-dependent and temporal manner in response to cellular stress induced by the cytotoxin okadaic acid in vitro. Following adeno-associated viral vector (AAV)-mediated delivery of a green fluorescent protein (GFP) reporter gene under control of the regulatory system to the rat substantia nigra pars compacta, expression of GFP was induced in response to cellular stress initiated in the striatum. In the final study the protective efficacy of the anti-apoptotic gene X-linked Inhibitor of Apoptosis Protein (XIAP) under the control of this system was examined in comparison to constitutive XIAP expression in the 6-OHDA model. The results showed that regulating XIAP expression with this system afforded greater protection of dopamine neurons in comparison to control animals that express GFP under control of the regulatory system. In contrast, the extent of dopamine cell loss in animals injected AAV vectors expression XIAP under control of a constitutively active promoter was not different to the corresponding control GFP vector-injected rats. Together these results provided proof-of-principle evidence of the utility of this system for the treatment of brain disorders associated with increased activation of proteases.

    View record details
  • 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.

    View record details
  • Scour at submerged weirs

    Guan, Dawei (2015)

    Doctoral thesis
    The University of Auckland Library

    Weirs or bed sills are river training structures that are used for raising upstream water level, bed stabilization and reducing flow velocity. During high flow events, the weir is fully submerged in the river and scouring occurs both upstream and downstream of the weir. Many empirical scour equations have been proposed for prediction of scour depth downstream of unsubmerged weirs. Research on scour at submerged weirs is very limited. For a fully submerged weir, the scour mechanism around the weir is dependent on approach flow intensity (clear-water scour conditions or live-bed scour conditions) and flow regimes (surface flow regime or impinging jet regime) over the weir. Under livebed scour conditions, the rapid evolution of underwater mobile topographies and propagating bedforms increases the complexities of the scour process and the difficulties for scour measurement at the submerged weir. The aim of this study is to experimentally investigate flow structures and scour process at submerged weirs in sand channels. The experimental programmes were conducted in a tilting recirculating flume. Both clear-water scour and live-bed scour conditions were applied. The experimental results of an investigation of flow structures at the weir show that a large recirculation zone and a flow reattachment region are formed downstream of the submerged weir. Strongly paired cellular secondary flows were observed in the scour hole. The turbulence structures ahead of the recirculation zone govern the dimensions of the scour hole downstream of the weir. In the coarse sand tests, bed elevation changes were measured in the approach flow reach and in the scour zones both upstream and downstream of the weir using a Seatek multiple transducer array. The highly contaminated raw bed-elevation data were filtered using a data processing technique. In the fine sand tests, the scour process was monitored using Logitech HD webcams on both sides of the flume. Image analysis was implemented to obtain bed profiles and scour depths over time. Under clear water scour conditions, the temporal development of maximum scour depth downstream of the weir has three stages: 1) initial fast stage, 2) progressing stage, 3) equilibrium stage. Under live bed scour conditions, the scour occurs both upstream and downstream of the weir, and sediment transport processes are highly influenced by strong turbulence in the vicinity of the submerged weir. A scour-and-fill process occurs immediately upstream from the weir in response to periodic approaching bed-forms. The dimensions of the scour hole downstream of the weir fluctuate due to the unsteady upstream sediment input and the development of secondary flows. The flow regimes over the submerged weir are found to be independent of the sediment size, and the transition flow regime boundary can be expressed as a function of upstream Froude number and the ratio of weir height to tailwater depth. On the basis of the experimental data, equations for prediction of equilibrium scour depths both upstream and downstream of the submerged weir are proposed. A design method is given in this study for estimating the maximum scour depths at the submerged weir.

    View record details
  • Sense Shaping Place: Interaction of Planning Actor???s Values in Social- Ecological Resilience: Case Study of Urbanizing Coastal Rural Communities in Pontian, Malaysia.

    Azizui, Muhammad Farid Azizul (2016)

    Doctoral thesis
    The University of Auckland Library

    Drawing on the literature from bioregional planning that encapsulates theories on place, stewardship and conservation, this study explores the dynamics in the interaction between the various planning actors and how this contributes to the resilience of socio-ecological systems (SESs). Using the urbanizing coastal rural communities of Pontian as a case study, I have employed a mixed-methods approach to examine the sense of place held by three distinct planning actor groups involved in the local land use planning activities. The groups are Local Active Community, Civic and Institution, and Environmental and Cultural Advocacy. I analyzed qualitative interviews as well as quantitative surveys to elicit the sense of place structure across groups, the relationship between structures and stewardship attitudes and behaviors, and examined how these characteristics might shape the trajectories of landscape change. This study extends the examination of the people-place relationship and its impacts on resilience, as prior place research has focused on sense of place at the individual level but is limited when assessing group level outcomes. A number of distinctions were found. The sense of place structure was found to be comprised of four traits; place dependence, place identity, place attachment and community attachment. The latter appeared to emerge separately. The structure patterns were similar across groups in the survey, however, a more nuanced description in the interviews revealed that the place structure for each of the first two groups emphasized social and community aspect of place, while the latter emphasized functional aspect of place dependency. The relationship between sense of place, stewardship and visions was far more complex than reported in the literature, where stewardship was divided between affirmative and non-supportive attitudes towards rural landscape change. In contrast, in this study ???place dependence??? correlated with ???concerned but supporting attitude??? and was characteristic of the first two groups. The qualitative findings specified that this variability between groups is linked to specific worldviews and motivations and visions that are layered in social, cultural and political backgrounds. Multiple pathways to sustainability were observed from different place conception and attitudes among the groups, based on analysis that is grounded in a model of SES and resilience. The insights were critiqued in a bioregional planning context and justify further research on sense of place as an integrative concept for understanding societal impacts on ecosystems in a complex, rapidly changing world. Keywords: bioregional planning, sense of place, environmental stewardship, socialecological resilience, landscape change.

    View record details
  • Transport Capacity Improvement in and around Ports: A Perspective on the Empty-container-truck Trips Problem

    Islam, Md (2014)

    Doctoral thesis
    The University of Auckland Library

    The problem of capacity shortage is an important issue for the major ports of the world. In particular, there is an increased necessity for additional transport capacity for containerised goods travelling to and from the hinterland (the region served by the port). For such travel, transportation using roads is often more popular than other methods (e.g., rail). A potential mechanism to increase road-side transport capacity is to lessen the number of empty truck trips by transferring increased numbers of containers using the same number of trucks. This forms the key Research Question (RQ) for this thesis. Namely, how can the number of empty container truck trips to and from a port be reduced to increase the road transport capacity? To date, much of the existing literature on the empty trips issue has been largely of an analytical nature (e.g., the backhaul problem) and thus has generally disregarded the potential benefits of the idea of involving all of the parties concerned in the container transport chain. To bridge that research gap, this thesis extends the shared-transportation concept, which is already proving popular in other areas (car-sharing and bike-sharing systems, for example), to the maritime logistics domain, in the form of truck-sharing. For this reason, the overall thesis work involves a combination of different research methodologies, which may be either qualitative (e.g., exploratory) or quantitative (e.g., simulation). However, before diving into the specifics of empty truck trips, the thesis looks broadly at capacity shortages at ports and particularly at how can a port's capacity be improved? Therefore, a system-dynamics framework is produced based on a review of the factors influencing port capacity, to guide and improve overall port capacity (including, but not limited to, transport capacity). The thesis also shows the potential usefulness of the suggested framework as an operational tool for capacity-expansion decisions (e.g., transport capacity improvement). In support of the question of reducing empty container truck trips, the thesis has four supporting research questions. First, RQ1 is: What are the different mechanisms available in different disciplines and domains for reducing empty truck trips? One of the key findings for this question is the prospect of using the truck-sharing concept for container transportation. RQ2 is: Is it possible to introduce a dynamic truck-sharing facility for a computer-based matching system to reduce empty truck trips? This research question further applies and extends the truck-sharing concept. Therefore, the model developed to answer this question is referred to as a Truck-sharing Service (TSS). However, the successful implementation of the suggested truck-sharing model depends on truck-sharing constraints that have not been fully explored. Therefore, RQ3 is: What are the truck-sharing challenges in achieving a higher level of collaboration among carriers to gain optimal container-truck utilisation and how to best overcome those challenges? Research findings show that port-related attributes, such as a lack of flexibility in the truck appointment system, form constraints against truck-sharing. Finally, to quantify the effect of the truck-sharing model on the potential for the improvement of transport capacity and its related carbon emission saving possibilities, RQ4 is: How will the case study port???s transport capacity be affected by different scenarios? Simulation results show improvement in performance using the truck-sharing idea. In particular, the truck-sharing concept boosts port gate- and transport-capacity, handles the increasing future truck volume effectively, and decreases carbon emissions generated from container trucks. The findings of this thesis work have important implications for the study of both freight transportation and maritime logistics in the reduction of the number of empty trips made by container trucks; this thesis provides theoretical grounds for practical ways of understanding and reforming the containerised cargo transportation process for road carriers. The aim is to increasing freight transport capacity and achieving sustainable transportation benefits at the port.

    View record details
  • An Ethnography of Everyday Practices: Young IT Professionals??? Engagement with Technologies

    Chughtai, Hameed (2015)

    Doctoral thesis
    The University of Auckland Library

    Information Systems (IS) research deals with the nature of information technology (IT) in our practices. The problem is that we, including IS researchers and practitioners, find ourselves deeply absorbed in our everyday practices. The fact that we tend to take our practices for granted makes discovering the logic of these practices an elusive enterprise. How, then, can we study these practices? In an attempt to furnish critical interpretations of the nature of our interaction with IT in our everyday practices, I used ethnographic research to study the practices of young tech savvy people (sometimes called ???digital natives???) because in their everyday lives they are always absorbed in ubiquitous IT phenomena. The ethnographic fieldwork began with a simple overarching question: how do young IT professionals interact with technologies in their everyday practices? It was envisioned that the ethnographic fieldwork would disclose deeper layers of meaning underlying practices of epistemic and ontological significance in terms of engagement with technology. Indeed, following the entwinement perspective of Martin Heidegger, I found that people are increasingly getting entwined with IT in their everyday practices; but further, entwinement can be seen as a ludic phenomenon, that is to say a play-like engaged absorption in one???s everyday being in the world. Technology is thus disclosed as an ordinary plaything in their practice worlds. Further, I found that when engaged absorption is seen as play, practices are bounded by everyday spaces where many playing fields are constantly being created by the players. In the final phases of ethnography, spatiality was discovered as a significant aspect of the field enquiry: how can an ethnographer make sense of a play-like engaged practice in which, and precisely where he or she is already absorbed in the field? The latter half of the fieldwork was thus focused on the examination of the spatial field that envelops the phenomenon where a technological practice is grounded. This thesis adopts a ???thesis with publications??? model and includes six original articles. The thesis also suggests some strategies to make sense of everyday practices, design practices, and the management of the younger workforce. Finally, the study aims to contribute to the ethnographic toolkit by suggesting the use of novel methodological tools such as ???thrownness???, play or ???ludic practices???, ???entwinement??? and ???spatial volatility??? of the fieldwork.

    View record details
  • 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.

    View record details
  • AGEing Peptides: Synthesis and Analysis of Peptides Site-Specifically Modified by Advanced Glycation Endproducts

    Kamalov, Meder (2014)

    Doctoral thesis
    The University of Auckland Library

    Advanced Glycation Endproducts (AGEs) are a family of modified amino acids that form when proteins react with sugars and sugar degradation products. AGEs are commonly found in processed food as well as in human organs, where they accumulate in tissue proteins, such as collagen, during the normal process of ageing. AGE accumulation dramatically accelerates with the onset of diabetes mellitus and the associated hyperglycaemia, a condition in which levels of sugars and sugar degradation product are above those considered healthy. Relative quantities of AGEs in different organs correlate with the pathophysiologic changes in these organs that occur with both advanced age and long-term hyperglycaemia. Emerging evidence indicates that AGE levels not only correlate with organ damage but may also play a causative role in such damage. Increased chelation of copper ions appears to play an important role in this process. However, the precise impact of AGE formation and accumulation on the biochemical properties of the host proteins is yet to be determined. Given their possible role in the detrimental outcomes of ageing (discussed in Chapter 1), in-depth studies of the AGE biochemistry are necessary. The overall aim of this work was to enable such in-depth studies of the AGE biochemistry by providing access to synthetic peptides that can be site-specifically modified by particular AGEs. Five prominent lysyl AGEs, N??-carboxymethyllysine (CML), N??-carboxyethyllysine (CEL), pyrraline, glyoxal lysine dimer (GOLD), and methylglyoxal lysine dimer (MOLD), were selected as targets. Synthesis of AGE building blocks, suitably protected for peptide incorporation, is discussed in Chapter 2. Efficient synthetic strategies were developed to provide access to all five AGE building blocks N??-protected by 9-Fluorenylmethoxycarbonyl (Fmoc) group. Synthesis of Fmoc-CML and Fmoc-CEL was accomplished using a facile and practical approach that involved the Fukuyama amino alkylation methodology. Fmoc-pyrraline was synthesised using an efficient pyrrole introduction protocol. Cross-linked building blocks, Fmoc2GOLD and Fmoc2MOLD, were prepared in the Debus-type amino-cyclisation procedure. Incorporation of the AGE building blocks into peptides is discussed in Chapter 2. Collagen, since it is a major target of glycation, was used as a source of synthetic peptides. By use of solid phase peptide synthesis, peptides mimicking the quaternary structures of collagen were prepared with and without AGEs. Incorporation of the CML, CEL, and pyrraline building blocks into collagen model peptides and collagen telopeptides was successfully carried out using Fmoc solid phase peptide synthesis protocol. A straightforward and cost-effective synthetic procedure to access CML-containing peptides via on-resin N-alkylation of lysyl amines has also been developed. Importantly, conditions for efficient incorporation of the lysyl AGE cross-links, GOLD and MOLD, have been successfully developed and employed in the first syntheses of crosslinked collagen model peptides and collagen telopeptides. Access to site-specifically glycated peptides has enabled us to probe the biochemical properties of glycated peptides (discussed in Chapter 4). Circular dichroism revealed that the introduction of monolysyl AGEs did not hamper the formation of triple helices by collagen model peptides. However, introduction of cross-linking AGEs effectively prevented the collagen model peptides from forming the triple helical structure. Studies of proteolytic digestion using trypsin have revealed the dramatic effect that introduction of lysyl AGEs had on the relative enzymatic digestion rates of the host peptides. These AGEs effectively prevented trypsin from digesting the host telopeptides. Our potentiometric study of copper binding by collagen telopeptides with and without CML has shown that introduction of CML dramatically increased the host peptides capacity to bind copper. Mass spectrometric analysis effectively confirmed the results of potentiometric measurements and provided the first direct evidence of increased copper binding by an AGE-modified peptide.

    View record details