33 results for Doctoral, Use commercially

  • "I just find it awkward": Girls' negotiations of sexualised pop music media

    Goddard, Sarah (2016)

    Doctoral thesis
    Victoria University of Wellington

    This thesis examines girls’ relationship with and consumption of female pop stars’ music media. It is contextualised within a period of extensive academic and media debate about girls’ engagement with what has been termed the sexualisation of culture. Much of the alarm concerning girls’ premature sexualisation is underpinned by the presumption of girls as passive media consumers who are uniformly influenced by sexually saturated female pop music, particularly its ubiquitous representation of hyper (hetero) sexually desiring femininity. The notion of girls as precociously sexualised by hypersexual female pop music media has gained homogenous status within mainstream media and popular psychology texts. Girls’ pleasurable consumption and negotiation of a sexually laden media landscape is approached in this research as complicated by their contradictory positioning as savvy consumers within the postfeminist girlhood consumer market and simultaneously as victims within mainstream media and academic literature. Grounded in feminist poststructuralist understandings of girls’ subjectivity, the thesis explores the possibilities of self that representations within female pop music media enable and constrain for girls. Furthermore, the thesis explores ways in which girls make sense of these discourses while carefully managing their positioning as consumers. The research upon which this thesis is based has two parts. Part one of the research involved focus groups within which 30 pre-teen girls, identifying as ‘Kiwis’ or ‘New Zealanders’ discussed their engagement with female popular music media. The second part comprises a thematic discursive and semiotic analysis of girls’ self-recorded group video performances to a favourite pop song by a female artist. Discursive analysis of the professional music videos on which girls’ performances were based accompanied analyses of girls’ videos. The thesis contributes to a growing body of critical feminist research which responds to sexualisation claims that underpin hegemonic understandings of contemporary girlhood. The analyses presented in the research challenge moralistic notions of girls as uniformly influenced by pop music media by highlighting their navigation of this media as a contradictory process of appropriation and rejection. This complex negotiation, while seen in previous feminist literature, is uniquely captured within this thesis through the innovative employment of a performance method that extends feminist theorisations which problematise binary assumptions of girls’ engagement with sexualised media. This research identifies girls’ meaning making as a contradictory and plural process and provides novel insights about girls’ negotiation of postfeminist femininities in their own self-making in relation to self. Crucially, the thesis highlights the way in which girls’ navigation of sexualised media can be understood as occurring through both rejection and reproduction of postfeminist femininity ideals. Contextualised in New Zealand, the research extends knowledge about girls’ navigation of sexualised media beyond a US/UK social context. It also advances the small body of New Zealand literature about girls’ media engagement broadly and about the ways they experience sexualised media in particular.

    View record details
  • Seismic investigations of the lithosphere in an amagmatic back-arc region: North Island, New Zealand

    Dimech, Jesse-Lee (2016)

    Doctoral thesis
    Victoria University of Wellington

    New seismic constraints on crustal and upper mantle structures, kinematics, and lithospheric rheology are reported from an amagmatic back-arc region: the southwest North Island of New Zealand. Robust earthquake locations reveal a hypocentre 'downwarp' beneath the east-west trending Taranaki–Ruapehu Line. These earthquakes occur in the uppermost mantle, at depths of 30–50 km, and are distinct from shallower 8–25 km-deep earthquakes near Mt. Ruapehu in terms of focal mechanisms and principal stress directions. A receiver function CCP stack shows that the mantle earthquakes occur beneath a large change in crustal thickness, where the Moho 'steps' from 28 to 35 km-deep and the steepest part of that step has a 20–50° dip. The mantle earthquakes are dominated by strike-slip fault movement and have a maximum compressive stress direction of NE–SW. The existence of mantle earthquakes beneath a steeply-dipping Moho step implies some sort of dynamic modication is occurring in the mantle lithosphere. One possibility to explain these features is the convective removal of the mantle lithosphere due to a Rayleigh–Taylor-type instability. South of the Taranaki–Ruapehu Line, the Moho conversion weakens on both the receiver function CCP stack, and marine seismic reflection data under most of the Wanganui Basin (SAHKE02 and GD100 seismic lines). However, localised bright reflections at Moho depths can be seen in both near-vertical and wide-angle seismic data. Attribute analysis of near-vertical seismic reflections suggests that the rocks beneath the reflectivity are strongly-attenuating (Q ~20) with a negative velocity contrast relative to the lower crust. These observations are interpreted to be related to the presence of serpentinite (antigorite) and/or high pore fluid pressures in the mantle wedge. The links between hydration of amagmatic back-arcs, serpentinisation and/or high pore fluid pressures, rock viscosity, and mantle instabilities are documented here for the southwest North Island of New Zealand. These associations may be applicable to other amagmatic back-arcs around the world.

    View record details
  • Learning Feature Selection and Combination Strategies for Generic Salient Object Detection

    Naqvi, Syed (2016)

    Doctoral thesis
    Victoria University of Wellington

    For a diverse range of applications in machine vision from social media searches to robotic home care providers, it is important to replicate the mechanism by which the human brain selects the most important visual information, while suppressing the remaining non-usable information. Many computational methods attempt to model this process by following the traditional model of visual attention. The traditional model of attention involves feature extraction, conditioning and combination to capture this behaviour of human visual attention. Consequently, the model has inherent design choices at its various stages. These choices include selection of parameters related to the feature computation process, setting a conditioning approach, feature importance and setting a combination approach. Despite rapid research and substantial improvements in benchmark performance, the performance of many models depends upon tuning these design choices in an ad hoc fashion. Additionally, these design choices are heuristic in nature, thus resulting in good performance only in certain settings. Consequentially, many such models exhibit low robustness to difficult stimuli and the complexities of real-world imagery. Machine learning and optimisation technique have long been used to increase the generalisability of a system to unseen data. Surprisingly, artificial learning techniques have not been investigated to their full potential to improve generalisation of visual attention methods. The proposed thesis is that artificial learning can increase the generalisability of the traditional model of visual attention by effective selection and optimal combination of features. The following new techniques have been introduced at various stages of the traditional model of visual attention to improve its generalisation performance, specifically on challenging cases of saliency detection: 1. Joint optimisation of feature related parameters and feature importance weights is introduced for the first time to improve the generalisation of the traditional model of visual attention. To evaluate the joint learning hypothesis, a new method namely GAOVSM is introduced for the tasks of eye fixation prediction. By finding the relationships between feature related parameters and feature importance, the developed method improves the generalisation performance of baseline method (that employ human encoded parameters). 2. Spectral matting based figure-ground segregation is introduced to overcome the artifacts encountered by region-based salient object detection approaches. By suppressing the unwanted background information and assigning saliency to object parts in a uniform manner, the developed FGS approach overcomes the limitations of region based approaches. 3. Joint optimisation of feature computation parameters and feature importance weights is introduced for optimal combination of FGS with complementary features for the first time for salient object detection. By learning feature related parameters and their respective importance at multiple segmentation thresholds and by considering the performance gaps amongst features, the developed FGSopt method improves the object detection performance of the FGS technique also improving upon several state-of-the-art salient object detection models. 4. The introduction of multiple combination schemes/rules further extends the generalisability of the traditional attention model beyond that of joint optimisation based single rules. The introduction of feature composition based grouping of images, enables the developed IGA method to autonomously identify an appropriate combination strategy for an unseen image. The results of a pair-wise ranksum test confirm that the IGA method is significantly better than the deterministic and classification based benchmark methods on the 99% confidence interval level. Extending this line of research, a novel relative encoding approach enables the adapted XCSCA method to group images having similar saliency prediction ability. By keeping track of previous inputs, the introduced action part of the XCSCA approach enables learning of generalised feature importance rules. By more accurate grouping of images as compared with IGA, generalised learnt rules and appropriate application of feature importance rules, the XCSCA approach improves upon the generalisation performance of the IGA method. 5. The introduced uniform saliency assignment and segmentation quality cues enable label free evaluation of a feature/saliency map. By accurate ranking and effective clustering, the developed DFS method successfully solves the complex problem of finding appropriate features for combination (on an-image-by-image basis) for the first time in saliency detection. The DFS method enables ground truth free evaluation of saliency methods and advances the state-of-the-art in data driven saliency aggregation by detection and deselection of redundant information. The final contribution is that the developed methods are formed into a complete system where analysis shows the effects of their interactions on the system. Based on the saliency prediction accuracy versus computational time trade-off, specialised variants of the proposed methods are presented along with the recommendations for further use by other saliency detection systems. This research work has shown that artificial learning can increase the generalisation of the traditional model of attention by effective selection and optimal combination of features. Overall, this thesis has shown that it is the ability to autonomously segregate images based on their types and subsequent learning of appropriate combinations that aid generalisation on difficult unseen stimuli.

    View record details
  • Improving Clustering Methods By Exploiting Richness Of Text Data

    Wahid, Abdul (2016)

    Doctoral thesis
    Victoria University of Wellington

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

    View record details
  • An investigation of foreign exchange risk management by exporting small and medium sized enterprises

    Dang, Vu (2015)

    Doctoral thesis
    Victoria University of Wellington

    Previous studies on foreign exchange (forex) risk management have tended to focus on multinational enterprises; while how SMEs manage their forex risk is still largely unexplored. As small and medium sized enterprises (SMEs) are increasingly involved in international markets, they have become a new research setting on forex risk management. Given that SMEs have limited access to resources, skills and capabilities, internal hedging techniques could be favoured by SMEs. There is limited research on this matter, and the extant literature on forex management generally considers derivatives as major hedging techniques for large firms. This thesis primarily investigates how exporting SMEs manage forex risk. In addition, approaches to forex management could be changed as a firm becomes more experienced internationally. Following the basic principles of internationalisation theory, the thesis also examines the impact of the internationalisation degree of the firm on forex management decisions. This thesis sheds new light on SMEs’ hedging practices by providing a better understanding of SMEs’ choices of forex risk management. Three research questions have been raised: (1) what determinants influence SMEs’ choice to hedge as a way of managing forex risk; (2) what strategies do SMEs use when they choose hedging to manage forex exposure; and (3) how does the degree of internationalisation impact the choice of forex management. The thesis draws on two theoretical perspectives to help address these overarching questions. It extends the use of the resource-based view (RBV), and combines this with internationalisation theory. The setting of SMEs is a context for using the RBV. New Zealand and Australian exporting SMEs provide the sample for testing the hypotheses. The contributions of this thesis are twofold. Firstly, the thesis identifies four determinants of forex risk strategy by exporting SMEs, i.e. degree of internationalisation (specifically, export ratio), forex exposure, perceived forex risk, and resources. Secondly, it extends the use of the RBV and the internationalisation theory in forex risk management of SMEs. In addition, the thesis uses a research approach combining an exploratory qualitative study and a main quantitative study.

    View record details
  • Factors Influencing Participant Satisfaction with Free/Libre and Open Source Software Projects

    Chawner, Brenda (2011)

    Doctoral thesis
    Victoria University of Wellington

    The purpose of this research was to identify factors that affect participants’ satisfaction with their experience of a free/libre open source software (FLOSS) project. The research built on existing models of user satisfaction from the information systems literature, and also incorporated two characteristics of FLOSS projects first identified by Ye, Nakakoji, Yamamoto, and Kishida (2005), product openness and process openness. The central research question it answered was, What factors influence participant satisfaction with a free/libre and open source application software project? Richard Stallman’s reasons for setting up the GNU project and the Free Software Foundation arose from his frustration at being forced to be a passive user of software used for a Xerox printer. These suggest that being able to be an active participant in a FLOSS project is one factor that should be examined, and therefore the first sub-question this project answers is, What types of contributions do participants make to free/libre and open source software projects? Several studies have shown that the extent of participation in a FLOSS project varies from individual to individual, and this variation leads to the second sub-question, Do the factors that influence satisfaction vary for different types of participation? If so, in what way? A preliminary conceptual model of factors affecting participant satisfaction was developed, reflecting the key concepts identified in the literature. The main theoretical goal of this research was to test the model using empirical data. The research used a sequential, mixed methods approach. The first, qualitative stage involved reviewing documents from selected projects and interviewing a purposive sample of FLOSS project participants. The second, quantitative stage involved an online survey of FLOSS project participants, and the data gathered were used to test the conceptual model. The results of the first stage showed that participation in FLOSS projects was a more complex construct than previously reported in the literature. Seven distinct categories of activities were identified: • use; • interaction with code; • supporting the community; • outreach; • sponsorship; • management; and • governance. Four attributes that modified these categories were also identified: organisational focus, role formality, remuneration, and time commitment. Data from 154 responses to the online survey were used to test the model using stepwise multiple regression, which determined the effect of each of the variables on overall participant satisfaction. Moderated regression analysis was used to test the effects of three potential moderating variables. The results showed that that perceived system complexity had the largest effect, decreasing satisfaction if respondents perceived that the software was complex, while project openness and perceived developer communication quality accounted for the most variance in satisfaction. The main theoretical contribution of this research lies in its extension of satisfaction studies to FLOSS communities, showing that communication and openness are more important than in conventional software projects. Its practical contribution will help people involved in the management and governance of FLOSS projects to identify ways of increasing their participants’ satisfaction, which may in turn encourage them to contribute more.

    View record details
  • Self-improvement books: A genre analysis

    Koay, Dong Liang (2015)

    Doctoral thesis
    Victoria University of Wellington

    The aim of the thesis is to explore the characteristics of self-improvement books as a genre. Although self-improvement books are a widely read genre, particularly in the Western world, none to my knowledge has examined the linguistic features of this genre in detail. The thesis draws on the three main schools of genre theory: English for Specific Purposes, Systemic Functional Linguistics, and the New Rhetoric, and begins by investigating the sections (e.g., acknowledgement, introduction chapter) in self-improvement books and the typicality of the sections. Focusing on three sections: introduction chapters, body chapters, and about the author sections, the thesis examines how authors structure the sections by analysing the moves and steps. This study also examines the stories in self-improvement books by analysing the purpose of the stories and their structure. Stories were chosen because they seemed to be a feature of self-improvement books based on my observation and as suggested by interview data. To analyse self-improvement books at a register level, the thesis examines the most unambiguous aspects of engagement: personal pronouns focusing on you, imperative clauses, and questions. It also examines the lexicogrammatical features of self-improvement book titles and compares them to the titles of historical biographies, showing that imperative clauses and ing-clause are found only in self-improvement book titles. Drawing on interview data and literature on the American Dream, American individualism, Neoliberalism, and New Age beliefs, the thesis explains how the linguistic characteristics of the genre of self-improvement books reflect these ideologies. The dataset for the study is 40 self-improvement books, selected on the basis of a set of criteria that I developed. Subsets were selected from the main dataset for specific analyses. The text analysis part of the study is supplemented by interview data from specialist informants, who come from three categories: readers of the genre, non-readers of the genre, and authors of the genre. Move analysis identifies obligatory rhetorical moves and indicates that the main purposes of introduction chapters and about the author sections are persuading readers to read the book, and establishing credibility, respectively. Authors always persuade readers to read their books by listing reasons to read them. To demonstrate authors’ credibility, they refer to their areas of expertise. Unlike the introduction chapters and about the author sections, the body chapters have more than one obligatory rhetorical move. The body chapters present the problem that readers potentially experience, present the authors’ message, recommend practical applications, and encourage readers to apply them. From a genre perspective, the purpose of all the stories in my analysis is to illustrate the authors’ message. Register analysis, and drawing on interview data, suggests that authors use the personal pronoun you, imperative clauses, and questions to engage readers. The abundance of the personal pronoun you suggests that self-improvement books are a reader-oriented genre. The analysis of the imperative clauses using Halliday’s process types suggests that the main way to improve our lives, the authors recommend, is to change how we think. Finally, my thesis shows that the social purpose of self-improvement books is to help potential readers improve their lives, and the approach of improving one’s life has an individualistic orientation.

    View record details
  • First Principles Study of Ga₍₂₀₋x₎Alx⁺ Nanoalloys: Structure, Thermodynamics and Phase Diagram

    Ojha, Udbhav (2015)

    Doctoral thesis
    Victoria University of Wellington

    Nanoalloys (a finite framework of two or more metal atoms) represent a rapidly growing field owing to the possibilities of tuning its properties as desired for various applications. Their properties are size, shape, composition, chemical ordering, and temperature dependent, thereby offering a large playground for varied research motivations. This thesis documents the investigations on how the addition of aluminium affects the cationic gallium clusters, both in terms of geometric & electronic structure and thermodynamics, which have been observed to show greater-than-bulk melting behaviour for small sizes. A specific cluster size of 20 atoms is selected, Ga₍₂₀₋x₎Alx⁺, with the overall intention of creating a phase diagram which is the most reliable way to predict the phase changes in the system. All the first principles (density functional theory) based Born-Oppenheimer molecular dynamics calculations have been performed in the microcanonical ensemble. Melting behaviour is first studied in the pure Al₂₀⁺ clusters and then in three representative clusters of Ga₍₂₀₋x₎Alx⁺ series: Ga₁₉Al⁺, Ga₁₁Al₉⁺ and Ga₃Al₁₇⁺ clusters. We observe that all the three nanoalloy compositions show greater-than-bulk melting behaviour behaviour as well and in Ga₁₉Al⁺, specifically, Al prefers the internal sites, contrary to the previous arguments. We go on to complete the solid-liquid-like melting phase diagram using the calculated information and further propose a model of these greater-than-bulk melting clusters to be components of the corresponding bulk phases, whether metals or alloys, with additional size-dependent contributions added to it.

    View record details
  • A dual-trap optical tweezer approach to study emulsion droplet interactions

    Griffiths, Marjorie (2015)

    Doctoral thesis
    Victoria University of Wellington

    Foods are a highly complex form of soft condensed matter. Their complexity arises from a number of interrelated factors including the natural heterogeneity of raw materials, intricate composition, and the subtle changes in molecular interactions and micro-structural arrangements dictated by food processing and storage. It is highly important to understand the forces dictating the food structure as the assembly and organisation of major structural entities (i.e biopolymers, droplets, bubbles, networks, and particles) are responsible for the foods stability, texture, flow properties and more inclusively their organoleptic properties. The structural entities of foods exhibit numerous forms of self-organization and have significant structure complexity and dynamic behaviour on the mesoscopic length scales from 10 to 1000 nanometres. These dynamic weak interactions between the constituents define the organized state that ranges from simple spatial or temporal ordering to more intricate interactions making up the food microstructure. These interactions are often small in magnitude and are short ranged making them difficult to measure directly. Very few studies have been carried out on direct force measurements in foodstuffs. The focus of this research was to develop a dual-trap optical tweezer method to directly measure interactions between micrometre colloidal particles and ultimately to design an apparatus where interactions between less homogeneous systems, such as emulsion droplets could directly measured as a function of separation. As the name suggests, optical tweezers provide the ability to control the position of particles using a focused laser beam. The general concept of this method is to immobilise two particles in two separate optical traps and step one particle closer to the other stationary particle in a controlled fashion. The droplet’s movement is then recorded using a high-speed camera that provides near-to-real-time images of the particle’s positions. The particle’s positions are determined by a 3-D tracking algorithm developed in-house which determines the position of both particles to a precision of sub-pixel accuracy. The force exerted on each droplet (by the other one) can be extracted as it is proportional to the trap strength (pN/μm) and the displacement of the particle from the centre of the optical trap (μm). To demonstrate the optical tweezer method,the interactions between silica beads of a known size were measured as a function of bead separation. The measured force-distance curves agreed with the electrostatic component of the DLVO theory. Once the method was established it was applied at increasing salt concentrations (decreasing Debye lengths). Interestingly, a salt concentration was found beyond which the experimental data no longer agreed with the predictions of DVLO theory. Above 100 μM sodium chloride the Debye length was reduced to less than the Brownian fluctuations of the particles in the traps, which then dominated the apparent repulsion by restricting their particle trajectories, masking the actual nature of the electrostatic interactions. This resulted in force curves which fitted the exponential function, however, the fitted decay constant bore no resemblance to the actual Debye length. A diffusion experiment was designed to demonstrate the ability to measure interactions in multiple environments using the same pair of beads (at low salt concentrations where Debye lengths are faithfully recovered). The evolution of force-displacement curves was measured as the local salt concentration changed owing to the diffusion of salt from the interface and the results obtained were shown to agree with predictions based on a standard diffusion formalism. Applying the dual-trap optical tweezers method, successfully demonstrated with silica beads, to less homogeneous systems such as emulsion droplets presented challenges which showcased that emulsion design was critical as certain criteria had to be met in order to facilitate undertaking the tweezer experiments. These criteria include particle size (1-3 μm ), low polydispersity, and a reasonable refractive index mismatch between the droplet and continuous phase. In keeping with food systems a protein stabilised oil-in-water emulsion was chosen. Two popular emulsifiers, sodium caseinate and β-lactoglobulin, were investigated at different ionic strength, pH and homogenisation pressures and phase volumes. The emulsion chosen for direct force measurements was a sodium caseinate emulsion when prepared in a 100 mM phosphate buffer at pH 7.0, 60 wt. % soya bean oil and 0.04 wt.% protein which provided an adequate droplet size with minimal polydispersity. Interactions between pairs of sodium caseinate emulsion droplets were measured. Unlike for silica beads, the individual droplet size needed to be measured to deter- mine the surface-to-surface separation of droplet pairs. The droplet’s diameter was determined by measuring the restricted diffusion of the droplet in a weak optical trap and fitting the short time mean squared displacement behaviour to a Brownian motion simulation. It was found that the droplet size can be determined in this fashion to within 50 nm. Moving forward, the interactions between pairs of emulsion droplets were measured in water using the same method gleaned from the silica bead interaction study. The experimental data fitted well to the electrostatic force described by the DLVO theory with reasonable ζ-potentials extracted. To further demonstrate this dual optical tweezer method, interactions between the same pair of droplets were measured at increasing NaCl concentrations by means of diffusion. The expected trend has found to agree from calculations of increased local salt concentration based on a diffusion equation. At salt concentrations above 100 μm significant deviations in the force-curves were observed that may signal salt induced changes of the droplet’s interface or be attributed to the small magnitude of the force being within the noise. This warrants further investigation. In conclusion, the dual-trap optical tweezers have shown incredible potential to become a robust method to measure the interactions between droplets. This method has some clear advantages over current methods including that force, and spatial resolution is superior, sample preparation is straightforward, forces are measured in 3-dimensions, and the droplets are free in solution during measurement, not wetted on surfaces. Accordingly, dual-trap optical tweezer methodology has provided the ability to measure interactions to a precision that has not yet been achieved by any other method for the study of emulsion systems, which in itself is a major achievement. This method is another tool in the toolbox of a colloid chemist, food scientist and physicists to probe interactions in soft materials.

    View record details
  • Magnetic and electronic properties of iron-based superconducting systems

    Sambale, Sebastian (2015)

    Doctoral thesis
    Victoria University of Wellington

    This thesis is motivated by the large variety of high-temperature superconductors that contain iron in the superconducting layer. This number has grown rapidly since the discovery in 2008 of the iron-pnictides (and chalcogenides), where iron and arsenic form the superconducting layer. Also of interest are the iron-cuprate hybrid materials, where one out of three copper atoms is replaced by iron. The aim is to understand the superconducting, magnetic and electronic properties of these materials in respect to their iron content. This thesis describes some of these properties for the iron-pnictide compounds of CeFeAsO₁₋xFx and AFe₂As₂ (A=Ba, Sr), and for the ironcuprate hybrids of FeSr₂YCu₂O₆₊y and FeSr₂Y₂₋xCexCu₂O₁₀₋y. Here it has been found that CeFeAsO₁₋xFx follows a 3D fluctuation conductivity above the superconducting transition and the thermal activation energy is correlated to the critical current density within a two fluid-flux creep model below the superconducting transition. NMR measurements show that there is considerable charge disorder within the superconducting doping region. The AFe₂As₂ show a positive magnetoresistance, which could be interpreted through three-carrier transport. Superconducting samples of SrFe₂As₂ display a large enhancement in the magnetoresistance below the superconducting transition up to 1600 %, which is due to three-carrier transport through metallic and superconducting regions in an inhomogeneous state. The superconducting properties of the iron-cuprate FeSr₂YCu₂O₆₊y in respect to the location of iron was studied under the influence of electron and hole doping and with additional magnetic impurities. FeSr₂Y₂₋xCexCu₂O₁₀₋y shows a disorder induced spin-glass state and strong localization depending on the doping.

    View record details
  • The glacial history of Tongariro and Ruapehu volcanoes, New Zealand

    Eaves, Shaun (2015)

    Doctoral thesis
    Victoria University of Wellington

    Understanding the drivers and mechanisms of past, natural changes in Earth’s climate is a fundamental goal of palaeoclimate science. Recent advances in cosmogenic surface exposure dating and numerical glacier modelling have greatly improved the utility of geological glacial records for palaeoclimatic reconstruction. Here, I apply these techniques to investigate the timing and magnitude of late Quaternary mountain glacier fluctuations on Tongariro massif and Mt. Ruapehu volcanoes in central North Island, New Zealand (39°S). First, I constrain the local cosmogenic ³He production rate, in order to compare my subsequent ³He moraine chronologies with other well-dated palaeoclimate records. I present a new radiocarbon age for a large debris avalanche event on the northwest slopes of Mt. Ruapehu that occurred at 10.4-10.6 cal. ka BP. Cosmogenic ³He concentrations in surficial boulders deposited during this event are consistent with that predicted by a global compilation of similar production rate calibrations. Thus, I conclude that this globally compiled production rate is suitable for cosmogenic ³He exposure age calculations in New Zealand. Exposure ages from moraine boulders on both volcanoes constrain the timing of two periods of glaciation during the last glacial cycle, when the termini of valley glaciers reached c. 1200 m asl. The most recent of these events occurred between c. 31-17 ka, which corresponds with the global Last Glacial Maximum. During this period, the local equilibrium line altitude was depressed by c. 800-1100 m. Numerical model simulations of the glaciers, using a coupled energy balance/ice flow model, suggest that local atmospheric temperature was 4-7 °C colder than present. This palaeotemperature estimate is not greatly impacted by post-glacial topographic change on these active volcanoes. Surface exposure ages from a degraded lateral moraine on Tongariro massif indicate that an earlier period of glaciation, of similar extent to that at the LGM, culminated during Marine Isotope Stage 4. During the last glacial-interglacial transition (c. 18-11 ka), glacial retreat on Mt. Ruapehu was interrupted by a re-advance during the late-glacial (c. 15-11 ka). Exposure ages for this event exhibit some scatter, likely due to surface processes. Accounting for these processes with a topographic diffusion model yields a best-estimate age of 14-13 ka, corresponding to the Lateglacial reversal in New Zealand. Glacier model experiments indicate this re-advance resulted from a temperature lowering of 2.5-3.4 °C relative to present. Comparison with other proxy records suggests that this cooling was most pronounced during summer. Due to its lower elevation, it is unlikely that glaciers were present on Tongariro massif at this time. The results of this research provide the first direct age constraint and quantitative palaeoclimate reconstructions for late Quaternary glacier fluctuations in central North Island, New Zealand. The timing and magnitude of these changes are in good agreement with glacial records from the Southern Alps and South America. This suggests that glaciers in the southern mid-latitudes were responding to common climatic forcings at orbital- and millennial-timescales, during the last glacial cycle.

    View record details
  • Methods and Computational Techniques for Investigating and Monitoring Seismic Velocities in the Earth's Crust

    Shelley, Adrian (2015)

    Doctoral thesis
    Victoria University of Wellington

    This thesis is concerned with scrutinising the source, distribution and detectability of seismic velocity phenomena that may be used as proxies to study conditions in the crust. Specifically, we develop modelling techniques in order to analyse the directional variation of seismic wave speed in the crust and test them at Mt. Asama in Japan and Canterbury, New Zealand. We also implement both active source and noise interferometry to identify velocity variations at Mt. Ruapehu, New Zealand. Observations of temporal variation of anisotropic seismic velocity parameters at Asama volcano in Japan indicate that there is some process (or processes) affecting anisotropy, attributed to closure of microcracks in the rock as it is subjected to volcanic stress in the crust. To test this assertion, a 3D numerical model is created incorporating volcanic stress, ray tracing and estimation of the anisotropy to produce synthetic shear wave splitting results using a dyke stress model. Anisotropy is calculated in two ways; by considering a basic scenario where crack density is uniform and a case where the strength of anisotropy is related to dry crack closure from deviatoric stress. We find that the approach is sensitive to crack density, crack compliance, and the regional stress field. In the case of dry crack closure, modelled stress conditions produce a much smaller degree of anisotropy than indicated by measurements. We propose that the source of anisotropy changes at Asama is tied to more complex processes that may precipitate from stress changes or other volcanic processes, such as the movement of pore fluid. We develop a generalised anisotropy inversion model based on the linearised, iterative least-squares inversion technique of Abt and Fischer [2008]. The model is streamlined for use with results from the MFAST automatic shear wave splitting software [Savage et al., 2010]. The method iteratively solves for the best fitting magnitude and orientation of anisotropy in each element of the model space using numerically calculated partial derivatives. The inversion is applied to the Canterbury plains in the region surrounding the Greendale fault, using shear-wave splitting data from the 2010 Darfield earthquake sequence. Crustal anisotropy is resolved down to a depth of 20 km at a spatial resolution of 5 km, with good resolution near the Greendale fault. We identify a lateral variation in anisotropy strength across the Greendale fault, possibly associated with post-seismic stress changes. We perform active source and noise interferometry at Ruapehu in order to investigate potential seismic velocity changes and assess their use as a possible eruption forecasting method. Six co-located 100 kg ammonium nitrate fuel oil explosives were set off serially at Lake Moawhango, situated approximately 20 km south-east of Mount Ruapehu. Two methods of interferometry, using moving window cross correlation in the time and frequency domains, respectively, were applied to the recorded signal from each explosion pair in order to determine velocity changes from the signal coda waves. We identify possible diurnal velocity variations of ~ 0:7% associated with strain caused by the solid Earth tide. Synthetic testing of velocity variation recoverability was also performed using both methods. Interferometry of noise cross-correlations during the period was also performed using moving window cross correlation in the frequency domain. Analysis of velocity variations in the ZZ, RR and TT component pairs show little coherency. This, combined with results from synthetic testing that show that the frequency domain interferometry technique employed is unstable above velocity variations of 0.1%, indicate that the method may not be suitable for determining velocity variations at Ruapehu.

    View record details
  • A Critical Realist Study of Political Identity in Aotearoa New Zealand: Materiality, Discourse and Context

    Woodhams, Jay (2015)

    Doctoral thesis
    Victoria University of Wellington

    Political identity is a complex phenomenon that is generated within a rich sociocultural context. This thesis examines political identity in informal talk which is situated within a relatively under-explored context, New Zealand’s capital city and political centre, Wellington. Grounding the study within the critical realist model of stratified reality provides the philosophical motivation to explore multi-layered discourses alongside the extra-discursive referents that underpin them. The analysis centres on a model of identity, contra postmodernism, which shows that identities, while socially recognised in discourse, are articulated in reference to physical and social structures. I adopt a comprehensive multi-layered approach to discourse by examining the macro sociocultural influences that appear to pattern interaction across the country, the meso-level subnational discourses that influence dialogue at a more situated level and the micro-level interactional stances taken up in everyday communication. Discourse at all levels is implicated in the identities I examine in this thesis and it is against this backdrop that I unpack political identity into its indexed discourses and constitutive stance acts. Framed by my ethnographic immersion in the study context and drawing on in-depth semi-structured interviews with twenty-six individuals, I explore the way in which discourse and stancetaking are implicated in the genesis of the participants’ political selves. I first consider the extra-discursive context, including the geographical, economic and cultural structures that underlie New Zealand discourses. This is followed by detailed analysis of sociocultural discourse as it appears in talk. I identify egalitarianism and tall poppy as two related discourses which are embedded within the historical context of the country. I also explore four subnational discourses relating to Wellington city, including the political town, left-wing and small town discourses, which occur alongside a discourse of contrast. These sociocultural and subnational discourses influence much of the talk that occurs in reference to politics in Wellington and are thus implicated in political identity as it is generated in moment-by-moment interaction. To explore this in further detail I examine the micro-level of interactional discourse, more specifically the processes of stancetaking, in two detailed case studies. The two focus participants demonstrate prominent stance processes which I argue are central to much identity work: intersubjectivity, in which the stances of all those involved in the discussion interact in complex ways; and multiplicity, when participants take numerous stance directions that appear to contribute to different aspects of their identities. The intensive focus on the case studies, alongside analysis of the full discursive and extra-discursive context, provides a multi-layered and philosophically anchored approach that seeks to contribute to current understandings of and approaches to the study of discourse and identity.

    View record details
  • Vascular epiphyte assemblage structure and distribution patterns in the south-temperate zone

    Taylor, Amanda (2016)

    Doctoral thesis
    Victoria University of Wellington

    Vascular epiphytes, which are specialised to spend their entire life cycle within trees, are significant contributors to local ecosystem services. However, our current understanding of epiphyte distributions, co-occurrences, and general ecology lags far behind that of terrestrial plants. Furthermore, the majority of epiphyte research is undertaken in tropical forests, with comparatively few studies extending into temperate climates. As such, whether epiphytic plant assemblage structure varies geographically, or is influenced by area and isolation effects needs further scrutiny. In addition, how epiphytes are distributed in relation to host tree ontogeny and microclimates specific to south-temperate forests is poorly understood. Here, I attempt to bridge this gap by researching epiphyte distributions and assemblage structure in New Zealand, southern Chile, and Australia. In the first biogeographic study of epiphyte-host interactions, I determined if epiphyte-host network structure (i.e. nestedness, species co-occurrences, species specialisation) varied among New Zealand and Chilean temperate forests (Chapter 2). At the forest stand level, network structure was consistent with stochastic structuring, which suggests that dispersal and disturbances are important drivers of epiphyte distributions at a biogeographic scale. However, deterministic structure was observed in New Zealand networks with regards to nestedness (i.e. when specialists interact with generalists), which suggests that positive species interactions influence epiphyte distributions at a within-tree scale. Second, I determined whether the composition of plant communities residing in epiphytic birds’ nest ferns (Asplenium goudeyi) on Lord Howe Island, Australia, are influenced by fern size, isolation from a major propagule source and resident plant community richness (Chapter 3). Results suggest that plant communities are structured by dispersal. For one, there was a significant isolation effect on resident plant community richness. Additionally, wind-dispersed taxa were well represented in isolated ferns, while animal-dispersed taxa and taxa with no specific dispersal strategies were absent. This is the first study to test the combined effects of area, isolation and resident plant richness on epiphytic plant assemblage structure. Third, using Darwin’s geological theory of island ontogeny as a theoretical construct, I explored changes in epiphyte species richness throughout tree ontogeny (Chapter 4). Theoretical frameworks have helped bridge the gap between our understanding of vascular epiphytes and terrestrial plants, however, none have been implemented to guide investigations on epiphyte assemblage development. Based on the general features of island ontogeny, I found three stages of epiphyte assemblage development: (i) an initial stage where host trees are devoid of epiphytes, (ii) a second stage where trees acquire epiphytes into maturity, and (iii) a hypothetical stage where epiphyte assemblages follow a period of species decline following host tree mortality. In addition to these results, I found interspecific variation in the ontogenetic stage at which host trees become favourable for epiphyte establishment and the rate at which epiphyte assemblages develop. Lastly, I explored the systematic distribution of epiphytes and mistletoes in relation to microclimate gradients around the trunks of trees (Chapter 5). In addition, I tested the physiological responses of epiphytes and mistletoes to reductions in their most limiting resources to determine if the responses were consistent with their distribution patterns. The radial distributions of epiphytes and mistletoes were highly directional, and paralleled gradients of humidity, light and water. Additionally, the photochemical efficiency of epiphytes and CO₂ assimilation in mistletoe leaves decreased in plants growing in environments with lower water and light availability, respectively. However, mistletoe leaves still assimilated CO₂ in lower light conditions, which suggests a high plasticity of mistletoes to growing in a canopy environment. Despite over 120 years of recognising the importance of vertical microclimates on epiphyte distributions, this is the first systematic study of epiphytic plant distributions in relation to microclimate gradients around the trunks of trees. This thesis has increased our understanding of epiphytic plant assemblage structure, and how it is influenced by host tree species, isolation, area and resident plant species richness. In addition, this thesis has increased our understanding of the effect of host tree ontogeny and microclimate on epiphyte distribution patterns. Together, these studies may be built upon more broadly to further elucidate drivers of epiphyte assembly and distribution patterns.

    View record details
  • Human inspired robotic path planning and heterogeneous robotic mapping

    Williams, Henry (2016)

    Doctoral thesis
    Victoria University of Wellington

    One of the biggest challenges facing robotics is the ability for a robot to autonomously navigate real-world unknown environments and is considered by many to be a key prerequisite of truly autonomous robots. Autonomous navigation is a complex problem that requires a robot to solve the three problems of navigation: localisation, goal recognition, and path-planning. Conventional approaches to these problems rely on computational techniques that are inherently rigid and brittle. That is, the underlying models cannot adapt to novel input, nor can they account for all potential external conditions, which could result in erroneous or misleading decision making. In contrast, humans are capable of learning from their prior experiences and adapting to novel situations. Humans are also capable of sharing their experiences and knowledge with other humans to bootstrap their learning. This is widely thought to underlie the success of humanity by allowing high-fidelity transmission of information and skills between individuals, facilitating cumulative knowledge gain. Furthermore, human cognition is influenced by internal emotion states. Historically considered to be a detriment to a person's cognitive process, recent research is regarding emotions as a beneficial mechanism in the decision making process by facilitating the communication of simple, but high-impact information. Human created control approaches are inherently rigid and cannot account for the complexity of behaviours required for autonomous navigation. The proposed thesis is that cognitive inspired mechanisms can address limitations in current robotic navigation techniques by allowing robots to autonomously learn beneficial behaviours from interacting with its environment. The first objective is to enable the sharing of navigation information between heterogeneous robotic platforms. The second objective is to add flexibility to rigid path-planning approaches by utilising emotions as low-level but high-impact behavioural responses. Inspired by cognitive sciences, a novel cognitive mapping approach is presented that functions in conjunction with current localisation techniques. The cognitive mapping stage utilises an Anticipatory Classifier System (ACS) to learn the novel Cognitive Action Map (CAM) of decision points, areas in which a robot must determine its next action (direction of travel). These physical actions provide a shared means of understanding the environment to allow for communicating learned navigation information. The presented cognitive mapping approach has been trained and evaluated on real-world robotic platforms. The results show the successful sharing of navigation information between two heterogeneous robotic platforms with different sensing capabilities. The results have also demonstrated the novel contribution of autonomously sharing navigation information between a range-based (GMapping) and vision-based (RatSLAM) localisation approach for the first time. The advantage of sharing information between localisation techniques allows an individual robotic platform to utilise the best fit localisation approach for its sensors while still being able to provide useful navigation information for robots with different sensor types. Inspired by theories on natural emotions, this work presents a novel emotion model designed to improve a robot's navigation performance through learning to adapt a rigid path-planning approach. The model is based on the concept of a bow-tie structure, linking emotional reinforcers and behavioural modifiers through intermediary emotion states. An important function of the emotions in the model is to provide a compact set of high-impact behaviour adaptations, reducing an otherwise tangled web of stimulus-response patterns. Crucially, the system learns these emotional responses with no human pre-specifying the behaviour of the robot, hence avoiding human bias. The results of training the emotion model demonstrate that it is capable of learning up to three emotion states for robotic navigation without human bias: fear, apprehension, and happiness. The fear and apprehension responses slow the robot's speed and drive the robot away from obstacles when the robot experiences pain, or is uncertain of its current position. The happiness response increases the speed of the robot and reduces the safety margins around obstacles when pain is absent, allowing the robot to drive closer to obstacles. These learned emotion responses have improved the navigation performance of the robot by reducing collisions and navigation times, in both simulated and real-world experiments. The two emotion model (fear and happiness) improved performance the most, indicating that a robot may only require two emotion states (fear and happiness) for navigation in common, static domains.

    View record details
  • Channelisation of Noise through a Rhythmic Gird: Brutalist Mechatronic Sound-sculpture

    Zareei, Mo (2016)

    Doctoral thesis
    Victoria University of Wellington

    The aim of this thesis is to provide accessibility and appreciation for sounds that are conventionally perceived as non-musical or “noise”. Ordering the noise on a grid of metric rhythms, and underlining its materiality through an audiovisual mode of expression are the two main strategies employed. Using the medium of mechatronics, mechanically generated sonic by-products of technological developments are chosen as the focus sonic material. As a result, the output of this research extends what is known as glitch music outside the territory of amplified sound, to a realm where noise is created physically and acoustically. Based on these objectives, and following an investigation on the use of mechatronics in contemporary sound-based art, an ensemble of mechatronic sound-sculptures is designed and developed. Varying in terms of material, sound-generating mechanism, and sonic quality, the ensemble is divided into three different instrument-types, each of which is introduced, thoroughly described, and sonically evaluated. Next, three new audiovisual works are developed and realised utilising the mechatronic sound-sculptures, in order to turn into practice the ideas explored in this research. These compositions – which are all exhibited in competitive international symposiums – undertake the integration of mechatronics in three areas of sonic arts that are interconnected with the sound-sculptures. Furthermore, this thesis also establishes an aesthetic framework that formalises a significant body of contemporary sound art and music that, prior to this work, had suffered academic inattention. Probing the various parallels between the ideas developed in this thesis and Brutalist architecture, ‘sound-based brutalism’ is coined and formulated as an aesthetic underpinning for not only the academically marginalised works discussed, but also the work of the author. Lastly, two audiovisual projects (a performance and a series of ten installation pieces) are developed using the entire mechatronic sound-sculpture series in an effort to realise ‘sound-based brutalism’.

    View record details
  • Essays on Disaster Risk and Economic Development

    Karim, Azreen (2016)

    Doctoral thesis
    Victoria University of Wellington

    This thesis consists of four self-contained papers in the areas of disaster risk and economic development. Chapter One provides a qualitative survey of the empirical literature on the nexus among poverty, inequality and natural disasters. The last few years have seen an explosion of economic research on the consequences of natural disasters. This new interest is attributable first and foremost to a growing awareness of the potentially catastrophic nature of these events, but also a result of the increasing awareness that natural disasters are social and economic events. Here, we survey the literature that examines the direct and indirect impact of natural disaster events specifically on the poor and their impact on the distribution of income within affected communities and societies. With a meta-regression analysis of the existing literature on the impacts of disasters on households in Chapter Two, we observe several general patterns. Incomes are clearly impacted adversely, with the impact observed specifically in per-capita measures. Consumption is also reduced, but to a lesser extent than incomes. Poor households appear to smooth their food consumption by reducing the consumption of non-food items; in particular health and education, and this suggests potentially long-term adverse consequences. Given the limits of our methodology and the paucity of research, we find no consistent patterns in long-term outcomes. We place disaster risk to the poor within the context of sustainable development and future climatic change. Our objective In Chapter Three is to identify all of the directly observable determinants’ of publicly allocated and realized spending for disaster risk reduction (DRR) at the local government (sub-district) level in Bangladesh. We employ the Heckman two-stage selection model with detailed public finance and other data from 483 sub-districts (Upazilas) across the country. While some of our results conform with our priors, our estimations surprisingly find that government does not respond to the sub-district’s risk exposure as a factor affecting the DRR financing mechanism. This variable is consistently counter-intuitively statistically insignificant. The DRR regional allocations do not seem to be determined by risk and exposure, only weakly by vulnerability, nor even by more transparent political economy motivations. In Chapter Four, we examine the short-run economic impacts of recurrent flooding on Bangladeshi households surveyed in 2000, 2005 and 2010. In 2010 Household Income and Expenditure Survey (HIES), households answered a set of questions’ on whether they were affected by flood and its likely impacts. We identify two treatment (affected) groups by using the self-reported data and historical rainfall data based flood risk index. We estimate a difference-in-difference (DID) model to quantify the impacts on income, expenditure, asset and labour market outcomes and further extend our analysis to different income and expenditure brackets. Overall, we find robust evidence of negative impacts on agricultural income and expenditure. Intriguingly, the extreme poor (i.e. the bottom 15th quintile) experience significant positive impacts on agricultural income in the self-reported treatment case.

    View record details
  • Tama Samoa Stories: Experiences and Perceptions of Identity, Belonging and Future Aspirations at Secondary School

    Rimoni, Fuapepe (2016)

    Doctoral thesis
    Victoria University of Wellington

    This thesis investigates the experiences of twelve strong, articulate and thoughtful tama Samoa (Samoan boys) through their participation in secondary schools and lives outside the classroom and through the stories of others. The study looked at how the students enacted their identities as Samoans, as learners and as young men who are anticipating the future. The study is premised on the view that Pacific identities are fluid, diverse, multi-dimensional and include a range of different perspectives relating to social class, ethnicity, culture and gender. Such a view of identity as complex is not generally taken into consideration in the literature on educational success and achievement of Pacific students in New Zealand. The study employed a phenomenological qualitative design, using focus groups and semi-structured interviews by talanoa (conversations). As the study involved a group of indigenous tama Samoa, the Samoan fa’afaletui method was used. Participants were a group of twelve tama Samoa in three Wellington secondary schools and their twelve nominated persons. The study found that there are key aspects to making the experiences of tama Samoa positive and successful within the secondary school. These include acknowledging tama Samoa and their multiple identities while attending secondary school; supporting the development of a sense of belonging through everyday interactions with peers and teachers, and affirming the belief by tama Samoa that secondary school socialisation serves to help them make future decisions. This study argues that the experiences of tama Samoa are deeply embedded within wider social, economic and political trends. Indeed, their “voices” are shaped in part by these broader forces that construct and represent them as being historically “disadvantaged” and socio-economically “underserved.” Further, this study advocates for the diverse voices of tama Samoa, along with their experiences, stories, hopes, aspirations and dreams to be brought to light and placed alongside the official accounts of Pacific “disadvantage” to enable more balanced critical discourses taking place. It is hoped that this study will offer further insights into the experiences of tama Samoa in the New Zealand secondary school context, from which valuable knowledge is derived to inform and support schools in improving the New Zealand secondary school experiences of Samoan adolescent boys.

    View record details
  • Spectroscopic investigation of excitonic and charge photogeneration processes in organic photovoltaic cells

    Gallaher, Joseph (2016)

    Doctoral thesis
    Victoria University of Wellington

    Organic photovoltaic (OPV) cells show significant promise as a renewable energy resource capable of meeting the world’s large and growing energy needs. Increasing device efficiency is central to achieving an economically viable option for widespread applications. To this end, a better understanding of the structure and dynamics of the electronic excited states is needed. In particular, the mechanism by which excitons (electron-hole pairs) escape their Coulombic attraction and generate photocurrent is yet to be established. In this thesis ultrafast laser spectroscopy, in particular transient absorption and time-resolved photoluminescence, are used to study: exciton relaxation, morphological effects on charge separation, and the pathway leading to triplet exciton states. In Chapter 3, a series of oligothiophenes are synthesised with well-defined conjugation lengths to act as molecular models of polymer backbone sub-units, and thereby probe exciton relaxation processes. Time-resolved photoluminescence (TRPL) and transient absorption (TA) spectroscopy measurements presented in Chapter 4 reveal emission signatures evolve from a mirror image of absorption - which lacks vibronic structure - towards a spectrally narrower and vibronically structured species on the hundreds of femtosecond to early picosecond timescale. Analysis of this spectral evolution shows that a broad distribution of torsional conformers is driven to rapidly planarize in the excited state, including in solid films. This provides evidence that both torsional relaxation and energy migration could contribute to the non-mirror image absorption-emission spectra observed in polymer thin films. Recently, long lived TA signatures have been attributed to triplet excited states with the suggested formation pathway being similar to organic light emitting diodes, whereby non-geminate (bimolecular) charge recombination leads to the formation of both singlet and triplet states. Isolated oligothiophenes in solution provide an ideal model system to investigate the role of structural relaxation on triplet exciton formation. Through analysis of TA spectral dynamics in Chapter 5, singlet and triplet exciton populations were tracked. Restriction of the torsional relaxation increased triplet yield suggesting vibrational hot states could drive triplet formation. This model could aid in understanding triplet exciton formation in polymer-based solar cells via spin-mixing instead of non-geminate recombination. In a series of polymer:fullerene blends, the link between the nature of polymerfullerene intermixing and charge generation pathways was investigated. It is shown in Chapter 6 that free charge generation is most efficient in a 3-phase morphology that features intimately mixed polymer:fullerene regions amongst neat polymer and fullerene phases. Distinct spectroscopic signatures made it possible to determine whether holes occupy disordered or crystalline polymer chains. TA spectral dynamics reveal the migration of holes from intermixed to pure olymer regions in 3-phase morphology blends, which contrasted with observations in 2-phase blends. The energy gradient between the intermixed and phase-pure regions may be sufficient to drive efficient separation of charge pairs initially generated in intermixed regions, with free charges subsequently percolating through these phase-pure domains. The photophysics of a high performance polymer:polymer blend is studied in Chapter 7 in an effort to elucidate how these blends can rival their polymer:fullerene counterparts. Optical spectroscopy reveals incomplete exciton dissociation and rapid geminate recombination in the blends. This is shown to result from a largely phase-separated morphology with domains greater than the exciton diffusion length. Significant loss of charge carriers on early timescales highlights increasing polymer: polymer solar cell efficiency requires optimizing blend morphology to realise facile charge separation. Taken together, this thesis presents a valuable spectroscopic insight into the pathway of efficient charge separation and the importance of both blend morphology and polymer structure.

    View record details
  • Professional Learning and Development (PLD) in Higher Education: The experiences of teacher educators in Vietnam

    Tran, Hue (2016)

    Doctoral thesis
    Victoria University of Wellington

    A key challenge for educators in Vietnamese higher education (HE) lies in the implementation of top-down national educational reforms. Professional learning and development (PLD) is viewed by the government as a primary means to enhance lecturers’ capacity to implement national educational initiatives. However, the nature of PLD for lecturers and its roles in supporting HE reforms in developing countries like Vietnam remain under-investigated. This study explores the practices of PLD for English as a foreign language (EFL) lecturers who are teacher educators within higher education, and the social, cultural, and political contexts within which these occur. The study employs a mixed-methods research methodology with a focus on qualitative approach and the use of Cultural Historical Activity Theory (CHAT) as the framework of analysis. A case study across three tertiary institutions provides the basis for an analysis of the phenomenon of PLD for EFL lecturers in Vietnam involving academic leaders and EFL lecturers. Complementary data collection methods were used: a questionnaire, individual semi-structured interviews, observations of PLD sessions, and relevant document review. Data were analysed both deductively and inductively to explore the roles of PLD in the educators’ personal and professional growth, and their capacity to enact mandated initiatives in the selected institutions. The findings indicate that PLD is a complex, political and culturally situated phenomenon that plays a key role in supporting the professional aspirations of lecturers. The study foregrounds the lecturers’ PLD experiences, the implications of PLD, and the influence of government and institutional policies and initiatives on the lecturers’ PLD. This study proposes a model of PLD that raises critical questions about how HE institutions and policy makers might provide a supportive PLD environment to better foster lecturers’ capacity to bring about changes at both personal and institutional levels. This model shows that PLD needs to be viewed across diverse forms including formal, collaborative and informal PLD. For PLD to be effective, consideration should be given to ensuring lecturers experience it as: (1) needs-based, relevant and meaningful for their learning and applicable to their teaching contexts, (2) encouraging them to be active and self-regulated learners, (3) promoting reflective and experiential learning, and (4) based on negotiated understandings of the purpose and function of PLD among all involved stakeholders. The study contributes to an understanding of PLD requirements for EFL teacher educators in an Asian context, and may be relevant to PLD for tertiary lecturers in a wider international context.

    View record details