Studies in Computational Plasma Physics

The scope of this work spans computational plasma simulation and modeling using state-of-the-art numerical and machine learning methods. The numerical work discussed involves performance and correctness modeling of two massively scalable heterogenous code bases. A gyrokinetic code used to simulate a plasma subjected to a strong magnetic guiding field and a particle-in-cell code used for simulating high energy density plasmas in a number of scenarios undergoing magnetic reconnection. Both code bases are capable of being distributed to cpu or gpu based compute nodes. The gyrokinetic code was used to study microinstabilities and turbulence in the edge region of a magnetically confined fusion device. Plasma confinement in such a device is partially due to the configuration of a poloidal magnetic field. It has been shown in experiment that a flipping of the magnetic field orientation may help reduce edge region turbulence, thus reducing the possibility of a catastrophic disruptions. Here a gyrokinetic code was used to study the edge region and the effect of poloidal field configuration on microinstability driven anomalous transport. The particle-in-cell numerical method of plasma physics balances a trade-off between computational cost and intrinsic noise. Inference on data produced by these simulations generally consists of binning the data to recover the particle distribution function, from which physical processes may be investigated. In addition to containing noise, the distribution function is temporally dynamic and can be non-gaussian and multi-modal, making the task of modeling it difficult. Here, the particle-in-cell code was used to produce data which was used with normalizing flow deep learning methods to learn a smooth, tractable approximation to the noisy particle distribution function. It is demonstrated that the resulting data driven likelihood conserves relevant physics and may be extended to encapsulate the temporal evolution of the distribution function. An alternative to particle-in-cell and gyrokinetic models are multi fluid models. The inclusion of kinetic effects into fluid models has been a long standing problem in magnetic reconnection and plasma physics. Generally the pressure tensor is reduced to a scalar which is an approximation used to aid in the modeling of large scale global systems such as the Earth\u27s magnetosphere. This unfortunately omits important kinetic physics which have been shown to play a crucial role in collisionless regimes. The multi-fluid 10-moment model on the other-hand retains the full symmetric pressure tensor. The 10-moment model is constructed by taking moments of the Vlasov equation up to second order, and includes the scalar density, the vector bulk-flow, and the symmetric pressure tensor for a total of 10 separate components. Use of the multi-fluid 10-moment model requires a closure which truncates the cascading system of equations. Here we look to leverage data-driven methodologies to seek a closure which may improve physical fidelity of the 10-moment multi-fluid model in collisionless regimes. Specifically we use the Sparse Identification of Nonlinear Dynamics (SINDy) method for symbolic equation discovery to seek the truncating closure from fully kinetic particle-in-cell simulation data, which inherently retains the relevant kinetic physics. We verify our method by reproducing the 10-moment model from the PIC particle data and use the method to generate a closure truncating the 10-moment model which is analyzed through the nonlinear phase of reconnectio

Productivity tradeoffs and synergies for grazing lands in central Queensland to generate carbon offsets

This paper reports research seeking to understand the economic implications for central Queensland graziers of participating in a carbon trading scheme and to measure the likely participation of graziers in an emissions trading scheme under various market design scenarios. An initial desktop study was undertaken to compare an enterprise which produced only cattle to one which produced cattle and sequestered carbon. The findings from this analysis were used to inform the design of an experimental auction to test alternative carbon trading scenarios. An experimental workshop was conducted at seven locations across central Queensland with a range of beef producers, extension officers and consultants. Participants were presented with a scenario in which they had the choice of maintaining current management practices against altering management practices to reduce beef production and enter into a carbon sequestration contract (CSC). They were asked at what price they would enter into a CSC and how that price and likelihood of participating would change under a range of alternative contract conditions. The results of the experimental auctions found significantly higher than breakeven prices for carbon would be required before landholders would offer land as a carbon offset. Participation rates were influenced by price and also the carbon contract rules. Five rule changes were trialled and all were found to have a significant impact on reducing participation and increasing required payment levels.Farm Management,

Unravelling the economic and environmental tradeoffs of reducing sediment movement from grazed pastures

An undesirable consequence of grazing activities in eastern Australia is the quantity of sediment emptying into the Great Barrier Reef Lagoon. One of the challenges to reducing sediment loads stems from the lack of private incentives to improve land management practices. There is also a poor understanding of the financial implications resulting from the adoption of sustainable management practices, and, in particular the lack of scientific and economic knowledge linking on-farm management actions to catchment scale impacts. Bio-economic modelling has been used to identify the economic and environmental trade-offs encountered when grazing strategies are altered to reduce off-farm sediment movement from a black spear grass pasture in central Queensland.bioeconomic modelling, grazing, economic and environmental, Environmental Economics and Policy,

Consumer demands for organic and genetically modified foods

Issues concerning consumer demands for genetically modified and organic food remain topical. It is unclear how consumers perceive issues associated with food production such as food safety, environmental impacts or animal welfare. It is also unclear how consumers might value potential changes in those issues in regional and metropolitan centres. This paper reports on research using the choice modelling technique to estimate and compare consumer demand for genetically modified and organic foods in Australia. The case study considers tomatoes, milk and beef commodities. The results draw comparisons between the contribution of associated factors influencing consumer purchasing decisions in a regional and metropolitan city. The results are relevant to the current policy debate regarding the introduction of GM foods.Genetically modified, organic, demand, choice modelling, Crop Production/Industries, Demand and Price Analysis, Food Consumption/Nutrition/Food Safety,

Quasi-option values for enhanced information regarding genetically modified foods

Issues concerning the long-term environmental and health risks associated with the production of genetically modified foods remain highly topical in Australia. It is unclear how consumers values for a precautionary approach to the release of genetically modified crops compares to the opportunity costs of forgoing economic growth associated with the use of these technologies. In this paper, an application of the contingent valuation method is reported. That technique was used to estimate quasi-option values held by consumers regarding a potential five year moratorium on the use of genetic modification in Australian agriculture. The results are compared to the estimated opportunity costs of imposing such a ban o Queensland consumers.Quasi-option values, genetically modified organisms, contingent valuation, Agricultural and Food Policy, Research Methods/ Statistical Methods,

In Search of a Data Driven Symbolic Multi-Fluid 10-Moment Model Closure

The inclusion of kinetic effects into fluid models has been a long standing problem in magnetic reconnection and plasma physics. Generally the pressure tensor is reduced to a scalar which is an approximation used to aid in the modeling of large scale global systems such as the Earth's magnetosphere. This unfortunately omits important kinetic physics which have been shown to play a crucial role in collisionless regimes. The multi-fluid 10-moment model on the other-hand retains the full symmetric pressure tensor. The 10-moment model is constructed by taking moments of the Vlasov equation up to second order, and includes the scalar density, the vector bulk-flow, and the symmetric pressure tensor for a total of 10 separate components. Use of the multi-fluid 10-moment model requires a closure which truncates the cascading system of equations. Here we look to leverage data-driven methodologies to seek a closure which may improve physical fidelity of the 10-moment multi-fluid model in collisionless regimes. Specifically we use the Sparse Identification of Nonlinear Dynamics (SINDy) method for symbolic equation discovery to seek the truncating closure from fully kinetic particle-in-cell simulation data, which inherently retains the relevant kinetic physics. We verify our method by reproducing the 10-moment model from the PIC particle data and use the method to generate a closure truncating the 10-moment model which is analyzed through the nonlinear phase of reconnection

Assessing the economic impact of an emissions trading scheme on agroforestry in Australia’s northern grazing systems

Although agriculture generates a significant portion of Australia’s greenhouse gas emissions, it also has the potential to sequester large quantities of emissions through changed land use management such as agroforestry. Whilst there is an extensive amount of agroforestry literature, little has been written on the economic consequences of adopting silvopastoral systems in northern Australia. This paper reports the economic feasibility of adopting complimentary agroforestry systems in the low rainfall region of northern Australia. The analysis incorporates the dynamic tradeoffs between tree and pasture growth, carbon sequestration, cleared regrowth decomposition rates and livestock methane emissions in a bioeconomic model. The results suggest there are financial benefits for landholders who integrate complimentary agroforestry activities into existing grazing operations depending on the rules of the carbon accounting framework used.carbon sequestration, financial analysis, carbon accounting framework, Agroforestry, Resource /Energy Economics and Policy,

An Examination of University Paramedic Students' Enculturation into the Ambulance Service

This study explores student paramedics’ enculturation into a traditional NHS ambulance service trust. The research illustrates the many challenges and dichotomies which face neophyte paramedics as they go from a University classroom setting into their day-to-day clinical work placements. The challenges they face are not the result of individuals alone, rather they result from an inherent subculture ingrained within the organisational structures of the ambulance service and paramedic profession. This ethnography contributes to the social science literature on health and social care by presenting a sociological perspective of student enculturation, from the university classroom into an often chaotic working environment of the ambulance service. In this research, the way cultural meanings, institutionalised rules, professional identity and working practices determine the working behaviours in the subculture of paramedic practice are uncovered, as individual situations and experiences are contextualised. Drawing on the work of seminal authors and experts in the field, this research explores the subculture along with the hidden curriculum which gives rise to it, as it seeks to understand how and why this appears to hamper and impede the pedagogy experienced by students. This is not the pedagogy taught and encouraged in university, rather a pedagogy which arises out from the intricacies and nuances of the traditional working environment of the paramedic. The research steers the reader through a complex interplay of subcultural integration between experienced paramedics and students. The work draws on the peculiarity of the language, behaviours, values and working practices of paramedics and students to illustrate the subculture and hidden curriculum which is inherent in their day-to-day working practices. How students transpose what they learn in the university classroom setting to their clinical work placements is examined and unpacked to help illuminate how students contextualise the knowledge formally taught in the university learning environment, to that of the practice setting. Supported by a plethora of fieldnotes and interviews with students and paramedics, along with my reflective and reflexive accounts collected over a period of eighteen months, this research informs and contributes to the unfolding developments within the paramedic profession. The work acquaints the reader with a rich meaningful insight into the working customs and practices not seen by members of the public or portrayed by media representations

Validation of simple epidemiological or clinical methods for the measurement of body composition in young children

The present study aimed to determine the validity of simple epidemiological and clinical methods for the assessment of body fatness in preschool children. In 89 children (42 boys, 47 girls; mean age 4.1 SD 1.3y) measures of body fatness were made using total body water (TBW), dual energy x-ray absorptiometry (DXA), air displacement plethysmography (BODPOD) and skinfold thickness. Methods were compared by Bland–Altman analysis using TBW as the reference method, and by paired comparisons and rank order correlations. Bias for DXA was +1.8% body fat percentage units (limits of agreement +15.5% to -11.9%), bias for BODPOD was -3.5% (limits of agreement +18.9% to -5.9%) and bias for skinfolds using the Slaughter equations was -6.5% (limits of agreement +10.0% to –23.1%). Significant rank order correlations with TBW measures of fatness were obtained for DXA estimates of fatness (r=0.54, P=0.01), but not for estimates of fat by skinfold thickness (r=0.20, P=0.2) or BODPOD (r=0.25, P=0.1). Differences between both DXA and BODPOD and the reference TBW estimates of body fatness were not significant (P=0.06 and P=0.1 respectively); however, the difference in estimated body fatness between skinfold thickness and TBW was significant (P<0.001). Estimates of body fatness in preschool children were inaccurate at the level of the individual child using all the methods, but DXA might provide unbiased estimates and a means of making relative assessments of body fatness

Improved grazing management practices in the catchments of the Great Barrier Reef, Australia: Does climate variability influence their adoption by landholders?

The declining health of the Great Barrier Reef from diffuse source pollutants has resulted in substantial policy attention on increasing the adoption of improved management practices by agricultural producers. Although economic modelling indicates that many improved management practices are financially rewarding, landholders with dated management practices remain hesitant to change. This research involved bio-economic modelling to understand the variance in private returns for grazing enterprises across a climate cycle. Results show that financial returns to landholders can vary substantially across different 20-year periods of a climate cycle, demonstrating that the variability in expected returns may be an important reason why landholders are cautious about changing their management practices. Although previous research has separately identified financial returns and attitudes to risk and uncertainty of landholders as key influences on decisions concerning adoption of improved management practices, this research demonstrates that it is the interaction between these factors that is important to understand when designing policy settings. © Australian Rangeland Society