title: Recurrent concept drifts on data streams

authors: Gunasekara, N

subjects: computer science

abstract: In an era where machine learning permeates every facet of human existence, and data evolves incessantly, the application of machine learning models transcends mere data processing. It involves navigating constant changes exemplified by the phenomenon of concept drift, which often affects model performance. These drifts can be recurrent due to the cyclic nature of the underlying data generation processes, which could be influenced by recurrent phenomena such as weather and time of the day. Stream Learning on data streams with recurrent concept drifts attempts to learn from such streams of data. The survey underscores the significance of the field and its practical applications, delving into nuanced definitions of machine learning for data streams afflicted by recurrent concept drifts. It explores diverse methodological approaches, elucidating their key design components. Additionally, it examines various evaluation techniques, benchmark datasets, and available software tailored for simulating and analysing data streams with recurrent concept drifts. Concluding, the survey offers insights into potential avenues for future research in the field.

text: Recurrent concept drifts on data streams In an era where machine learning permeates every facet of human existence, and data evolves incessantly, the application of machine learning models transcends mere data processing. It involves navigating constant changes exemplified by the phenomenon of concept drift, which often affects model performance. These drifts can be recurrent due to the cyclic nature of the underlying data generation processes, which could be influenced by recurrent phenomena such as weather and time of the day. Stream Learning on data streams with recurrent concept drifts attempts to learn from such streams of data. The survey underscores the significance of the field and its practical applications, delving into nuanced definitions of machine learning for data streams afflicted by recurrent concept drifts. It explores diverse methodological approaches, elucidating their key design components. Additionally, it examines various evaluation techniques, benchmark datasets, and available software tailored for simulating and analysing data streams with recurrent concept drifts. Concluding, the survey offers insights into potential avenues for future research in the field.

year: 2024

title: Modelling New Zealand dairy farm systems to design greenhouse gas mitigation strategies

authors: Adler, Alfredo A.

subjects: mitigaiton cost

abstract: Dairy cattle in New Zealand account for about 17% of the country’s total greenhouse gas (GHG) load. As the nation progresses in its efforts to reduce these emissions, is likely that the dairy industry will face physical constraints and/or financial costs associated with their mitigation. For this study, a non-linear optimization model was developed to analyse the cost-effectiveness of diverse mitigation strategies for reducing GHG loads between 10–30% within systems of different production intensity in the main dairy farming regions of New Zealand: Waikato and Canterbury. Pastoral dairy farms, as found in New Zealand, are complex farming systems with many interdependent management variables and any change in one of these variables in order to reduce GHG emissions will inevitably affect the system as a whole, generating changes in its physical and economic outputs. Computer modelling is thus highly suited to evaluate alternative strategies, given its capacity to represent and consider these interdependencies simultaneously.
De-intensification, by reducing any combination of stocking rate, nitrogen fertiliser and supplement use, was a key strategy in reducing GHG emissions in an economic manner across the whole range of farming systems and regions considered in this study, as well as for all levels of emissions constraints tested. The mean farm profit reduction found under this level of mitigation across all studied systems was 6%, when no other mitigation strategies were available. To achieve this, the mean reduction in stocking rate was 8.8% and the mean nitrogen fertilizer reduction was 36%. Nitrogen fertiliser usage increases GHG emissions by increasing the available mineral nitrogen in soil and thus increasing denitrification and also by increasing enteric methane emissions as more fibrous feed is available to be consumed. The mean profit reduction was 6.9% and 4.9% for the Waikato and Canterbury regions, respectively.
The Canterbury medium-input system had a lower cost of mitigation than the other systems, associated with the use of more supplements with high embedded GHG emissions in the baseline. Accordingly, the use of this kind of supplement was quickly reduced by the optimization model in the mitigation scenarios. At the other end, the Canterbury high input system had the highest cost of mitigation, arising from a combination of larger GHG-e reductions required in absolute terms and the low profitability of the baseline plan, given its high use of imported supplement. In contrast, the abatement cost in the Waikato systems was intermediate between these two extremes.
Improved reproductive performance and improved genetic merit of the herd were selected as optimal in all cases where specific mitigation strategies were available. Profit was reduced by 1.6%, on average, in this case when 10% GHG emissions reductions were imposed. To adapt to this constraint, stocking rate was reduced by 8.1%, while N fertilizer was reduced by 30.7%, on average. Thus, although the availability of specific mitigation strategies was valuable in reducing the profit losses arising from mitigation, these were not sufficient to reduce emissions without some degree of de-intensification. 
Other mitigation strategies, like removing cows from pasture or the use of denitrification inhibitors, were not always cost effective and only entered the optimal solution when higher levels of mitigation were imposed. This demonstrates that the high cost of adopting these specific mitigation strategies is only warranted when systems are exposed to larger profit reductions associated with higher levels of de-intensification. A quick calculation using average reduction in milksolids production found in this study shows that the loss of revenue of the dairy industry if 30% mitigation of GHG is imposed can represent as much as half the export earnings of the entire beef industry of the nation.

text: Modelling New Zealand dairy farm systems to design greenhouse gas mitigation strategies Dairy cattle in New Zealand account for about 17% of the country’s total greenhouse gas (GHG) load. As the nation progresses in its efforts to reduce these emissions, is likely that the dairy industry will face physical constraints and/or financial costs associated with their mitigation. For this study, a non-linear optimization model was developed to analyse the cost-effectiveness of diverse mitigation strategies for reducing GHG loads between 10–30% within systems of different production intensity in the main dairy farming regions of New Zealand: Waikato and Canterbury. Pastoral dairy farms, as found in New Zealand, are complex farming systems with many interdependent management variables and any change in one of these variables in order to reduce GHG emissions will inevitably affect the system as a whole, generating changes in its physical and economic outputs. Computer modelling is thus highly suited to evaluate alternative strategies, given its capacity to represent and consider these interdependencies simultaneously.
De-intensification, by reducing any combination of stocking rate, nitrogen fertiliser and supplement use, was a key strategy in reducing GHG emissions in an economic manner across the whole range of farming systems and regions considered in this study, as well as for all levels of emissions constraints tested. The mean farm profit reduction found under this level of mitigation across all studied systems was 6%, when no other mitigation strategies were available. To achieve this, the mean reduction in stocking rate was 8.8% and the mean nitrogen fertilizer reduction was 36%. Nitrogen fertiliser usage increases GHG emissions by increasing the available mineral nitrogen in soil and thus increasing denitrification and also by increasing enteric methane emissions as more fibrous feed is available to be consumed. The mean profit reduction was 6.9% and 4.9% for the Waikato and Canterbury regions, respectively.
The Canterbury medium-input system had a lower cost of mitigation than the other systems, associated with the use of more supplements with high embedded GHG emissions in the baseline. Accordingly, the use of this kind of supplement was quickly reduced by the optimization model in the mitigation scenarios. At the other end, the Canterbury high input system had the highest cost of mitigation, arising from a combination of larger GHG-e reductions required in absolute terms and the low profitability of the baseline plan, given its high use of imported supplement. In contrast, the abatement cost in the Waikato systems was intermediate between these two extremes.
Improved reproductive performance and improved genetic merit of the herd were selected as optimal in all cases where specific mitigation strategies were available. Profit was reduced by 1.6%, on average, in this case when 10% GHG emissions reductions were imposed. To adapt to this constraint, stocking rate was reduced by 8.1%, while N fertilizer was reduced by 30.7%, on average. Thus, although the availability of specific mitigation strategies was valuable in reducing the profit losses arising from mitigation, these were not sufficient to reduce emissions without some degree of de-intensification. 
Other mitigation strategies, like removing cows from pasture or the use of denitrification inhibitors, were not always cost effective and only entered the optimal solution when higher levels of mitigation were imposed. This demonstrates that the high cost of adopting these specific mitigation strategies is only warranted when systems are exposed to larger profit reductions associated with higher levels of de-intensification. A quick calculation using average reduction in milksolids production found in this study shows that the loss of revenue of the dairy industry if 30% mitigation of GHG is imposed can represent as much as half the export earnings of the entire beef industry of the nation.

year: 2014

title: Images of Pakeha-Māori: A Study of the Representation of Pakeha-Māori by Historians of New Zealand From Arthur Thomson (1859) to James Belich (1996)

authors: Bentley, Trevor William

subjects: Pakeha-Maori

abstract: This thesis investigates how Pakeha-Māori have been represented in New Zealand non-fiction writing during the nineteenth and twentieth centuries. The chronological and textual boundaries range from Arthur Thomson's seminal history The Story of New Zealand (1859) to James Belich's Making Peoples (1996). It examines the discursive inventions and reinventions of Pakeha-Māori from the stereotypical images of the Victorian era to modern times when the contact zone has become a subject of critical investigation and a sign of changing intellectual dynamics in New Zealand and elsewhere.

This thesis is about the history of attitudes to culture-crossers in New Zealand, the use of the term 'Pakeha-Māori', and the images that underlie the thinking of Britons and Pakeha about them. It explores the motives and backgrounds of specific authors and the ways in which they frame New Zealand history. It elucidates the ambiguous and contradictory perspectives of Pakeha-Māori in the literature and analyses its impact on changing public perceptions about them. The study critiques the literature with emphasis on theoretically informed research, historical analysis, and literary insights. Discussion is confined to published texts, with the aim of exploring the multiplicity of Pakeha-Māori images and the processes that gave rise to them.

This study is essentially an investigation into how and why historians and other scholars try to draw boundaries between cultures in order to create a satisfactory metanarrative or myth of the 'settlement' of New Zealand and thus to forge a sense of New Zealandness. The cultural and racial categories of 'Māori' and 'Pakeha' are very unstable, however, and a consideration of the 'in-between' or 'culture-crossing' category of 'Pakeha-Māori' can reveal the way in which 'Māori' and 'Pakeha' and a sense of New Zealand and New Zealanders have been constructed. More particularly, consideration of representations of those culture-crossers or race-crossers called Pakeha-Māori can reveal the hopes and fears of Pakeha writers regarding Pakeha, Māori and New Zealand and how Pakeha-Māori have frequently been a barometer or litmus test of public perceptions of relations between Māori and Pakeha in different historical periods.

text: Images of Pakeha-Māori: A Study of the Representation of Pakeha-Māori by Historians of New Zealand From Arthur Thomson (1859) to James Belich (1996) This thesis investigates how Pakeha-Māori have been represented in New Zealand non-fiction writing during the nineteenth and twentieth centuries. The chronological and textual boundaries range from Arthur Thomson's seminal history The Story of New Zealand (1859) to James Belich's Making Peoples (1996). It examines the discursive inventions and reinventions of Pakeha-Māori from the stereotypical images of the Victorian era to modern times when the contact zone has become a subject of critical investigation and a sign of changing intellectual dynamics in New Zealand and elsewhere.

This thesis is about the history of attitudes to culture-crossers in New Zealand, the use of the term 'Pakeha-Māori', and the images that underlie the thinking of Britons and Pakeha about them. It explores the motives and backgrounds of specific authors and the ways in which they frame New Zealand history. It elucidates the ambiguous and contradictory perspectives of Pakeha-Māori in the literature and analyses its impact on changing public perceptions about them. The study critiques the literature with emphasis on theoretically informed research, historical analysis, and literary insights. Discussion is confined to published texts, with the aim of exploring the multiplicity of Pakeha-Māori images and the processes that gave rise to them.

This study is essentially an investigation into how and why historians and other scholars try to draw boundaries between cultures in order to create a satisfactory metanarrative or myth of the 'settlement' of New Zealand and thus to forge a sense of New Zealandness. The cultural and racial categories of 'Māori' and 'Pakeha' are very unstable, however, and a consideration of the 'in-between' or 'culture-crossing' category of 'Pakeha-Māori' can reveal the way in which 'Māori' and 'Pakeha' and a sense of New Zealand and New Zealanders have been constructed. More particularly, consideration of representations of those culture-crossers or race-crossers called Pakeha-Māori can reveal the hopes and fears of Pakeha writers regarding Pakeha, Māori and New Zealand and how Pakeha-Māori have frequently been a barometer or litmus test of public perceptions of relations between Māori and Pakeha in different historical periods.

year: 2007