Bifurcation Phenomena in Two-Dimensional Piecewise Smooth Discontinuous Maps

In recent years the theory of border collision bifurcations has been developed for piecewise smooth maps that are continuous across the border, and has been successfully applied to explain nonsmooth bifurcation phenomena in physical systems. However, many switching dynamical systems have been found to yield two-dimensional piecewise smooth maps that are discontinuous across the border. The theory for understanding the bifurcation phenomena in such systems is not available yet. In this paper we present the first approach to the problem of analysing and classifying the bifurcation phenomena in two-dimensional discontinuous maps, based on a piecewise linear approximation in the neighborhood of the border. We explain the bifurcations occurring in the static VAR compensator used in electrical power systems, using the theory developed in this paper. This theory may be applied similarly to other systems that yield two-dimensional discontinuous maps

The Passenger: Medieval Texts and Transits

What strange transactions take place in the mobile spaces between loci? How does the flow of forces between fixed points enliven texts, suggest new connections, and map out the dizzying motion of myriad interactions? The essays in this volume were first presented at the 2014 New Chaucer Society Congress in Reykjavik, Iceland where a meeting of minds in a shared intermediate space initiated dialogue from diverse perspectives and wended its way through the invisible spaces between concrete categories, objects, and entities. The resulting volume asks a core question: what can we learn by tarrying at the nexus points and hubs through which things move in and out of texts, attempting to trace not the things themselves or their supposedly stable significations, but rather their forms of emergence and retreat, of disorder and disequilibrium? The answer is complex and intermediate, for we ourselves are emerging and retreating within our own systems of transit and experiencing our own disequilibrium. Scholarship, like transit, is never complete and yet never congeals into inertia

Doctor of Philosophy

dissertationThe management of iconic predatory species such as the gray wolf provides a valuable index of human-nature relations. The wolf is incorporated into discursive constructions of political power in unique ways, and it may function as an ideograph, or an ideological discursive tool. As both a symbolic mobilizer of human sympathies/ antipathies and an influential material presence within ecosystems, the wolf is worthy of study for how its characterization in discourse resonates rhetorically and materially. This study uses discourse analytic tools to examine tensions in the rhetorical discourse of management decisions related to the gray wolf's reintroduction in the United States. The study focuses on the reintroduction and recovery of the gray wolf in the American West and considers broader themes related to the separation between humans and nature, wildlife management, and the ways in which human and nonhuman bodies alike are disciplined by the discourse of political borders. Engaging the concepts of territoriality, power, ideology and human-nature hybridity while working from specific findings regarding wolf characterization, this study explores how the wolf's presence is both enabled and constrained rhetorically by human political discourse regimes that may fragment the species as an ecological presence in bioregions by imposing on it a rhetoric of political borders

The value of animal behaviour as a bio-indicator of restoration quality

Woodland restoration is a complex endeavour, and restoration ecology as a scientific discipline requires constant re-assessments and adjustments if it is to improve outcomes and better provide for biodiversity. The promise of effective restoration is often used to justify destructive processes that affect many of the world’s ecosystems. It is therefore imperative that those promises can be met, which comes down to restoration ecologists’ and land managers’ capacity to predict and facilitate desirable ecological changes in a timely and socio-economically responsible manner. As perspectives have changed, and knowledge has been gained over the past few decades there have been several fundamental shifts in how restoration is done. Efforts to ‘beautify’ degraded areas through the planting of fast growing non-native species is no longer thought of as responsible restoration practice. We have a better understanding of ecological thresholds, the creation of novel ecosystems and the ways ecosystems move between stable states through transitional processes. Yet many restoration projects still fail to deliver positive outcomes for certain taxonomic groups. Fauna are an important component of biodiversity, and yet ecological filters and traps remain common in restored habitats. To date, the focus in restoration has been biased towards restoring flora, while fauna have been under-appreciated and under-utilised. This is likely due to a lack of clarity around how fauna can be used to assess restoration success. This study sought to address that issue by exploring ways fauna could be used to assess habitat quality, and evaluate whether they could fit into existing restoration management tools like a state-and-transition model. Variation in habitat quality was assessed using a number of biodiversity measures and behavioural patterns. This study used Rottnest Island in Western Australia, a mosaic landscape with a woodland restoration program that has been running for over 50 years. The Island’s woodland areas support a resident population of red-capped robins Petroica goodenovii, which was the focal species of this study. The robins are typically groundforaging insectivores that generally have been found to respond negatively to anthropocentric land use changes. The suitability of the Island’s robin population as an indicator for the larger avian community was assessed to determine whether management and monitoring could simply focus on improving conditions for robins. Unfortunately, robins were found to be a poor indicator of the larger avian community. Factors that were positively correlated with estimated robin density, like woodland area and time since last fire, were negatively correlated with density of other avian species of conservation significance. Invertebrate assembly was surveyed as a measure of food resource availability. There was a significant difference between woodland and heathland areas and to a lesser, but still significant, extent between restored woodland areas of different ages and remnant woodland. A major finding of this study was that Coleoptera were scarcely encountered in ground samples outside of remnant patches, but were among the most common orders in arboreal samples, specifically in old restoration. Given that this order is a major component of numerous insectivore diets, it is likely that this difference is influencing foraging habitat quality. This conclusion is supported by difference detected in the birds’ foraging behaviour, as birds in remnants foraged predominantly on the ground, while in restored areas birds were frequently observed collecting prey items from vegetation. Aside from changing their foraging behaviour, the birds were also found to rarely display breeding related behaviours while in restored habitat. This mimicked a significant difference in juvenile robin population density between restored and remnant patches during the breeding season. As such, it appears robins readily use restored areas for feeding resources, but remnants remain a crucial component of their functional habitat requirements, providing important breeding habitat. Behaviour was found to be a useful tool in explaining and verifying measured differences in habitat quality, and in this case, could easily be incorporated into pre-existing fauna monitoring programs. Robins weren’t found to be a suitable indicator species for the bird community, and given the small species pool on the island, management may need to consider all species of conservation significance separately

The practice of conservation management in rural-amenity landscapes: a dwelt human-environment perspective

Rural regions once dominated by productive agriculture in many post-industrial nations are experiencing an increasing transition towards non-productive land use. This transition has raised community and academic concern over potential environmental impacts to rural land. However, strong interest in conservation issues amongst rural-amenity in-migrants has supported a counter narrative of positive ecological implications. I argue there is a gap in this debate on the ecological implications of rural-amenity migration; limited attention has been paid to how amenity in-migrants actually practice land management on their property. To address this gap, the key question of my research is ‘How do social and landscape interactions shape the practices and outcomes of land management in rural-amenity landscapes?’ This work has implications for environmental policy amidst the changing land use and social dynamics of rural-amenity landscapes. This is particularly important in the face of increasing policy attention to conservation issues on private land. I concentrate on the growing political emphasis on voluntary conservation initiatives, addressing the limited understanding of how these programs are actually operationalised by landholders on the ground. To investigate the primary research question, an ethnographically-inspired case study project was undertaken in the hinterland regions of Melbourne, Australia. Narrative interviews and property-walks comprised the primary data collection methods. Interviews with staff involved in conservation policy, and reviews of policy documents provided supporting material. Landholders involved in three different voluntary conservation schemes (representing three distinct policy approaches) were targeted, as well as a non-participant cohort. My research found that the strong amenity values held by participants underscored individualised, property-centric management aspirations. This resulted in preferred channels for knowledge generation that favoured experiential learning and communities of practice. Little knowledge for informing management was shared between neighbours in an effort to avoid neighbourly conflict. Over time, this knowledge settled into a durable disposition for stewardship that reflected a prevailing tendency for either ‘active’ or ‘passive’ management. Dynamic ecologies were being created on private land as landholders navigated the tensions between their diverse aspirations for management and land use. This dynamism was seen in the way ecologies were spatially and temporally enacted; boundaries around the home were created through ornamental nature plantings, while the ‘bring back’ of indigenous nature through revegetation was mediated by non-conservation amenity values. In adopting voluntary conservation schemes, landholders were pursuing creative conservation outcomes that accord with existing practices and ecologies, often departing from the biodiversity-centric objectives of the schemes. Of key interest was the adoption of market-based schemes to enhance regulatory protection for vegetation, rather than for financial reward. In exposing landholders’ desires for social and ecological outcomes through program participation, I suggest the need for a more humanistic approach to conservation policy in rural-amenity landscapes. Overall, my research shows how the ecologies of rural-amenity landscapes embody a negotiation of amenity values and stewardship, as landholders come to establish a new rural lifestyle. Advancing nature conservation policy in this context requires consideration of the diverse and multiple ways in which landholders create and value these ecologies

2012 Research Day Abstract Listing

Abstracts of oral and poster presentations from student researchers, presented at UNC\u27s Annual Research Conference during Academic Excellence Week