Investigations of the Physical and Magnetic Microstructure of CoCr Thin Film Perpendicular Magnetic Recording Media

The work presented in this thesis is concerned with improving the understanding of the relationship between the physical and magnetic microstructure in CoCr thin film perpendicular magnetic recording media. This was investigated using a combination of transmission electron microscope (TEM) techniques to study a series of CoCr films with systematically adjusted growth conditions. The first chapter begins with an outline of basic ferromagnetism and the energy considerations governing the domain configuration in ferromagnetic thin films. General principles of magnetic recording are then discussed, with a more detailed treatment of media, high density recording formats and the properties of CoCr for perpendicular recording. Chapter 2 introduces basic TEM imaging theory and describes the conventional transmission electron microscopes (CTEM's) and the dedicated scanning transmission electron microscope (STEM) used in this project. The chapter then discusses techniques for imaging magnetic structures and the use of high resolution energy dispersive x-ray (EDX) microanalysis in the STEM for microcompositional investigations. The first sections in chapter 3 discuss the planar and cross-sectional specimen preparation techniques adopted for all the work in this thesis. The remainder of the chapter describes the study of a series of CoCr layers grown to various thicknesses and with different compositions. Bulk physical and magnetic characterisation are combined with microstructural investigations in the CTEM. The work demonstrates that bulk measurements alone are insufficient to predict the physical, and therefore the magnetic microstructure, of CoCr thin films. It also illustrates the usefulness of such a study as part of any investigation of the microscopic properties of CoCr recording media. The next three chapters contain the experimental results which form the core of the thesis. Chapter 4 describes the experiments conducted on CoCr films using EDX microanalysis. Planar sections were investigated to allow correct positioning of the probe on a particular region of specimen and thus reveal, directly, the local elemental composition associated with features of the microstructure. Study was made of films deposited at different substrate temperatures both with and without a Ge underlayer. The results obtained using this technique provided detailed quantitative data on the extent and pattern of Cr segregation in each film. Chapter 5 describes the improvements in the differential phase contrast (DPC) mode of Lorentz microscopy in the STEM which facilitated simultaneous imaging of the physical and magnetic microstructure of thinned cross-sections of CoCr films. The results from the application of this technique to the study of the effect on the microstructure of substrate temperature during deposition are then interpreted in conjunction with the compositional information from chapter 4. The importance of direct microscopic study of recorded tracks in CoCr perpendicular recording media forms the introduction for chapter 6. The chapter then explains the development and results of a successful method for direct observation of the tracks with the Fresnel mode of Lorentz microscopy in the JEOL 2000FX TEM. The final chapter draws conclusions on the results of the project and presents proposals for possible future investigations of CoCr perpendicular magnetic recording media

Managing ecological systems with unknown threshold locations

The optimal management of ecological systems is challenging because the locations of thresholds between desirable and undesirable regimes are generally unknown to the decision-maker. However, it is possible to learn about the resilience of an ecological system by intelligently perturbing the system using adaptive management (Arrow et al. 1995). Previous research has modelled optimal decisions in systems with hysteretic thresholds (Mäler et al. 2003), derived necessary conditions for optimal control when the locations of thresholds are unknown (Nævdal 2006; Nævdal and Oppenheimer 2007), and used stochastic dynamic programming to examine the effect of this form of uncertainty on risk averse behaviour (Brozovic and Schlenker 2011). This thesis extends previous research to model the effect on optimal decisions of learning about the locations of thresholds via a process of adaptive management. A dynamic programming framework is developed and applied to various ecological contexts, including numerical simulations of a shallow lake ecosystem, and used to demonstrate the role of learning. This thesis demonstrates that learning can be modelled by updating the prior probability distribution for a threshold’s location and by adjusting the boundary between the regions of a system’s state-space that could and could not contain the threshold. The model captures the trade-off faced by the decision-maker between the costs of crossing a threshold and shifting to an undesirable alternative regime, and the benefits of learning about the threshold location. Explicit consideration of the value of information means the decision-maker will generally make decisions that incur a greater risk of crossing the threshold in order to learn about its location. This finding is independent of the initial prior probability distribution used to model threshold location and the type of ecosystem dynamics considered. By explicitly modelling the value of information, this thesis better demonstrates the nature of optimal decision-making in the adaptive management of ecological systems

Managing ecological systems with unknown threshold locations

The optimal management of ecological systems is challenging because the locations of thresholds between desirable and undesirable regimes are generally unknown to the decision-maker. However, it is possible to learn about the resilience of an ecological system by intelligently perturbing the system using adaptive management (Arrow et al. 1995). Previous research has modelled optimal decisions in systems with hysteretic thresholds (Mäler et al. 2003), derived necessary conditions for optimal control when the locations of thresholds are unknown (Nævdal 2006; Nævdal and Oppenheimer 2007), and used stochastic dynamic programming to examine the effect of this form of uncertainty on risk averse behaviour (Brozovic and Schlenker 2011). This thesis extends previous research to model the effect on optimal decisions of learning about the locations of thresholds via a process of adaptive management. A dynamic programming framework is developed and applied to various ecological contexts, including numerical simulations of a shallow lake ecosystem, and used to demonstrate the role of learning. This thesis demonstrates that learning can be modelled by updating the prior probability distribution for a threshold’s location and by adjusting the boundary between the regions of a system’s state-space that could and could not contain the threshold. The model captures the trade-off faced by the decision-maker between the costs of crossing a threshold and shifting to an undesirable alternative regime, and the benefits of learning about the threshold location. Explicit consideration of the value of information means the decision-maker will generally make decisions that incur a greater risk of crossing the threshold in order to learn about its location. This finding is independent of the initial prior probability distribution used to model threshold location and the type of ecosystem dynamics considered. By explicitly modelling the value of information, this thesis better demonstrates the nature of optimal decision-making in the adaptive management of ecological systems

The interpretation and characterisation of lineaments identified from Landsat TM imagery of SW England

Two Landsat TM scenes of SW England and a sub-scene of North Cornwall have been analysed visually in order to examine the effect of resolution on lineament interpretation. Images were viewed at several different scales as a result of varying image resolution whilst maintaining a fixed screen pixel size. Lineament analysis at each scale utilised GIS techniques and involved several stages: initial lineament identification and digitisation; removal of lineaments related to anthropogenic features to produce cleansed lineament maps; compilation of lineament attributes using ARC/INFO; cluster analysis for identification of lineament directional families; and line sampling of lineament maps in order to determine spacing. SW England lies within the temperate zone of Europe and the extensive agricultural cover and infrastructure conceal the underlying geology. The consequences of this for lineament analysis were examined using sub-images of North Cornwall. Here anthropogenic features are visible at all resolutions between 30m and 120m pixel sizes but lie outside the observation threshold at 150m. Having confidence that lineaments at this resolution are of non-anthropogenic origin optimises lineament identification since the image may be viewed in greater detail. On this basis, lineament analysis of SW England was performed using image resolutions of 150m. Valuable geological information below the observation threshold in 150m resolution images is likely, however, to be contained in the lineament maps produced from higher resolution images. For images analysed at higher resolutions, therefore, knowledge-based rules were established in order to cleanse the lineament populations. Compiled lineament maps were 'ground truthed' (primarily involving comparison with published geological maps but included phases of field mapping) in order to characterise their geological affinities. The major lineament trends were correlated to lithotectonic boundaries, and cross-cutting fractures sets. Major lineament trends produced distinct frequency/orientation maxima. Multiple minor geological structures, however, produced semi-overlapping groups. A clustering technique was devised to resolve overlapping groups into lineament directional families. The newly defined lineament directional families were further analysed in two ways: (i) Analysis of the spatial density of the length and frequency of lineaments indicates that individual and multiple lineament directional families vary spatially and are compartmentalised into local tectonic domains, often bounded by major lineaments. Hence, such density maps provide useful additional information about the structural framework of SW England. (ii) Lineament spacing and length of the lineament directional families were analysed for the effect of scale and geological causes on their frequency/size distributions. Spacing of fracture lineaments were found to be power-law, whereas lengths showed power-law and non-power-law distributions. Furthermore the type of frequency/size distribution for a lineament directional family can change with increasing resolution

Risk Maps of Lassa Fever in West Africa

Previous studies on the eco-epidemiology of Lassa fever in Guinea, West Africa, have shown that the reservoir is two to three times more infected by Lassa virus in the rainy season than in the dry season. None of the intrinsic variables of the murine population, such as abundance or reproduction, was able to explain this seasonal variation in prevalence. We therefore here investigate the importance of extrinsic environmental variables, partly influenced by the idea that in the case of nephropathia epidemica in Europe contamination of the environment, and therefore survival of the pathogen outside the host, appears to be an important factor in this disease's epidemiology. We therefore made an extensive review of the literature, gathering information about the geographical location of sites where Lassa fever has been certainly identified. Environmental data for these sites (rainfall, temperature, vegetation and altitude) were gathered from a variety of sources, both satellites and ground-based meteorological stations. Several statistical treatments were applied to produce Lassa ‘risk maps’. These maps all indicate a strong influence of rainfall, and a lesser influence of temperature in defining high risk areas. The area of greatest risk is located between Guinea and Cameroon

The metabolic response of huhu larvae, prionoplus reticularis (coleopteran : cerambycidae) to stress from elevated temperature and reduced oxygen

Huhu, Prionoplus reticularis White (Coleoptera: Cerambycidae), are native New Zealand borers of quarantine importance. Huhu do not attack living trees, although their eggs can be laid on freshly-felled timber and larvae may be found in older export timber. To control insect pests, many logs from New Zealand are currently fumigated with methyl bromide (MBr), which has led to research to find alternatives for this ozone-depleting chemical. Treatments using heat and controlled atmospheres require a large amount of insect mortality data, often collected on a trial and error basis, which is time consuming and expensive. Insect physiological responses to treatment stress may complement mortality studies. These physiological studies on huhu sought to determine how huhu larvae respond to stresses caused by elevated temperature and low oxygen atmospheres. The purpose was to identify metabolic responses in huhu that could assist with development of commodity, insect disinfestation strategies. An artificial diet for huhu larvae was developed and tested for rearing uniform insects for physiological studies. Larvae were reared at 20 and 25°C and two day-lengths to identify suitable rearing conditions. The artificial diet was suitable for rearing huhu larvae at 20°C with either day-length. Rearing at 25°C shortened development time initially, but ultimately, larval weight decreased and many died. Huhu larvae had standard and active metabolic rates at 20°C of 1.66 and 4.42 μmol.kg⁻¹.s⁻¹, respectively as measured by manometric compensatory respirometry. Larval metabolic rate increased 1.72 times in response to a 10°C increase in temperature, over the range of 20 to 42°C. At temperatures greater than 35°C, larval movement ceased, consistent with stress responses reported for other insects. An automated gas analysis system was constructed and calibrated, which redirected the focus of planned research using the manometric system. SMR for huhu at 20- 40°C was lower than predicted values, but within the range of non-flying adult coleopterans and had a mass exponent between 0.62 and 0.67. The respiratory quotient (RQ) increased with temperature, suggesting a shift from metabolising fat to include other substrates. Activity increased larval metabolism but RQ was independent of activity at 20°C. Temperature sensitivity was similar when measured by gas analysis or manometrically. Huhu oxygen consumption ( ṀO₂ ) and carbon dioxide production ( ṀCO₂ ) were measured with the automated gas analysis system. .When larvae were exposed to extreme constant temperatures, 35-45°C, larval ṀO₂ increased until a critical temperature (42/43°C) resulted in falling ṀO₂ , which was exacerbated by time. ṀCO₂ reached a thermal maximum, suggesting the elimination of carbon dioxide may be a limiting factor. These changes in metabolism were consistent with mortality studies on huhu exposed to heat. Larval ṀCO₂ was reduced in 1.8% oxygen and movement ceased, suggesting huhu use metabolic depression to survive hypoxia. Recovery from anoxia increased ṀO₂ as larvae repaid an oxygen debt. Huhu haemolymph pH and lactate levels were measured after exposure to stress. Extreme temperature, reduced oxygen atmospheres and their combinations increased anaerobiosis, indicated by increased haemolymph acidosis and lactate. The metabolic response depended on the severity of the atmosphere-temperature treatment and exposure time. This study has successfully measured the metabolism of a larval cerambycid, and added valuable knowledge to the relative paucity of studies in this subject area. In response to stress, huhu larvae can utilise anaerobic pathways leading to severe acidosis with large amounts of lactate, in contrast to much of the published literature. The respiratory responses and increased anaerobic respiration found in this study, when an insect is exposed to stress, will assist the development of commodity disinfestation protocols and will contribute to a reduction the use of MBr

Natural resources of Lake Earl and Smith River Delta

The Lake Earl/Smith River Delta area is a key coastal wetland situated in northern California. The Lake and Delta have retained much of their value to wildlife and serve as an important link in a chain of such wetlands that extend southward along the Pacific Ocean from Alaska to South America. Millions of water-associated birds of the Pacific Flyway utilize these areas as feeding and resting stops along their migration paths. In California, these wetlands also serve as a significant portion of the available wintering grounds for a major share of the birds within the flyway. The Smith River is also one of the State's most productive salmon and steelhead streams. Anadromous fish produced here provide thousands of angler use days to sport fishermen and contribute substantially to the commercial fishing catch off the northern coast. Because of the importance of coastal wetlands to the fish and wildlife of California, the Department of Fish and Game has initiated a high priority statewide inventory and assessment of these wetlands. This publication is an integral part of that program. This report identifies specific resources and uses; directs attention to problems; and recommends courses of action needed to insure resource protection. It is intended as a guide for citizens, planners, administrators and other interested in the use and development of California's coastal land and waters. (132pp.