title: Magnetic energy release in dynamic fan reconnection models

authors: Craig, Ian J.D.

subjects: MHD—plasmas—sun

abstract: The problem of dynamic, three-dimensional magnetic reconnection is considered. Analytic “fan current” solutions are derived by superposing plane-wave disturbances on magnetic X-point equilibria. The localization of the wave produces a strong current sheet containing the neutral point. It is shown that the classical rate of resistive dissipation in the sheet, namely Wn~n1/2, represents the slowest possible energy-loss rate for the disturbance. The conditions required for fast coronal reconnection are then discussed. It is pointed out that significant “flare-like” energy release may be possible under physically realizable conditions. Moreover, the small length scales associated with the current sheet widths of order ∆x~n1/2 suggest that conditions are probably collisionless close to the neutral point. It is argued that our results are consistent with magnetic reconnection simulations that display “stalling” of the merging rate at small plasma resistivities.

text: Magnetic energy release in dynamic fan reconnection models The problem of dynamic, three-dimensional magnetic reconnection is considered. Analytic “fan current” solutions are derived by superposing plane-wave disturbances on magnetic X-point equilibria. The localization of the wave produces a strong current sheet containing the neutral point. It is shown that the classical rate of resistive dissipation in the sheet, namely Wn~n1/2, represents the slowest possible energy-loss rate for the disturbance. The conditions required for fast coronal reconnection are then discussed. It is pointed out that significant “flare-like” energy release may be possible under physically realizable conditions. Moreover, the small length scales associated with the current sheet widths of order ∆x~n1/2 suggest that conditions are probably collisionless close to the neutral point. It is argued that our results are consistent with magnetic reconnection simulations that display “stalling” of the merging rate at small plasma resistivities.

year: 1999-01

title: The role of the deposit feeding bivalve Macomona liliana in a simple biophysical model for predicting estuarine ecosystem tipping points

authors: Thomson, Taylor Scott

subjects: Macomona liliana

abstract: Estuaries are highly productive, coastal marine environments that provide vital ecosystem functions supporting human health. Throughout history, many major settlements have been established adjacent to estuaries, so to take advantage of the resources they provide. After centuries of exploitation and heavy pollution, the health of estuaries have experienced a notable decline. The need for effective management strategies has arisen, but their efficacy continues to be questioned due to the dynamic and unpredictable nature of these environments. Non-linear processes, such as regime shifts, make long-term predictions of ecosystem health a point of concern. To combat this issue in New Zealand, ecosystem interaction networks (EINs) have been used to predict the future health of estuaries using long-term statistical modelling. Unfortunately, these models fail to capture the coupling interactions between biotic and abiotic variables that occur in such a volatile environment. Therefore, we have created a simple model design that replicates the dynamic ecosystem interactions found within the benthic environments of New Zealand estuaries, with a specific focus on the behaviour of the keystone bivalve species Macomona liliana. A multitude of biophysical dynamical models currently exist in this field (e.g. Delft3D and DELWAQ); however none with the ability to replicate the exchange of nutrients between the sediment and benthic layer caused by M. liliana pumping behaviour. Consequently, this makes our model the first of its kind. Our model design simulates the variation of three dynamic variables (biomass, nutrients, detritus) corresponding to the interactions of M. liliana and microphytobenthos (MPB) at a representative site of New Zealand sandy bottom estuaries (Tuapiro Point, Tauranga Harbour). Extensive testing was conducted to ensure that, at the baseline level, the model’s output was consistent with field sampling data seen within the literature. Once completed, the model was tested against external forcing factors that are likely to occur within New Zealand estuaries – turbidity, sedimentation, and external nutrient loading. We found that our system is light limited, with M. liliana and MPB biomasses both declining with increasing turbidity. MPB populations fluctuate significantly following a sediment mud content increase, which we believe demonstrates a reaction to an ecological tipping point being surpassed. Furthermore, we found that a significant influx of external nutrient loading is required to initiate a MPB bloom, which the system cannot maintain despite nutrient levels remaining high. Our model’s results are in agreement with estuarine responses seen in the past, with our design exceeding the guidelines surrounding the efficacy in predicting ecosystem tipping points. Therefore, due to its unique ability to demonstrate the interactions within coupled systems and its broad applicability globally, we believe our model can become a central component of future estuarine management strategies. Recommendations are made for future improvements to the model design, increasing both its range of simulated ecological processes and the validity of its predictions.

text: The role of the deposit feeding bivalve Macomona liliana in a simple biophysical model for predicting estuarine ecosystem tipping points Estuaries are highly productive, coastal marine environments that provide vital ecosystem functions supporting human health. Throughout history, many major settlements have been established adjacent to estuaries, so to take advantage of the resources they provide. After centuries of exploitation and heavy pollution, the health of estuaries have experienced a notable decline. The need for effective management strategies has arisen, but their efficacy continues to be questioned due to the dynamic and unpredictable nature of these environments. Non-linear processes, such as regime shifts, make long-term predictions of ecosystem health a point of concern. To combat this issue in New Zealand, ecosystem interaction networks (EINs) have been used to predict the future health of estuaries using long-term statistical modelling. Unfortunately, these models fail to capture the coupling interactions between biotic and abiotic variables that occur in such a volatile environment. Therefore, we have created a simple model design that replicates the dynamic ecosystem interactions found within the benthic environments of New Zealand estuaries, with a specific focus on the behaviour of the keystone bivalve species Macomona liliana. A multitude of biophysical dynamical models currently exist in this field (e.g. Delft3D and DELWAQ); however none with the ability to replicate the exchange of nutrients between the sediment and benthic layer caused by M. liliana pumping behaviour. Consequently, this makes our model the first of its kind. Our model design simulates the variation of three dynamic variables (biomass, nutrients, detritus) corresponding to the interactions of M. liliana and microphytobenthos (MPB) at a representative site of New Zealand sandy bottom estuaries (Tuapiro Point, Tauranga Harbour). Extensive testing was conducted to ensure that, at the baseline level, the model’s output was consistent with field sampling data seen within the literature. Once completed, the model was tested against external forcing factors that are likely to occur within New Zealand estuaries – turbidity, sedimentation, and external nutrient loading. We found that our system is light limited, with M. liliana and MPB biomasses both declining with increasing turbidity. MPB populations fluctuate significantly following a sediment mud content increase, which we believe demonstrates a reaction to an ecological tipping point being surpassed. Furthermore, we found that a significant influx of external nutrient loading is required to initiate a MPB bloom, which the system cannot maintain despite nutrient levels remaining high. Our model’s results are in agreement with estuarine responses seen in the past, with our design exceeding the guidelines surrounding the efficacy in predicting ecosystem tipping points. Therefore, due to its unique ability to demonstrate the interactions within coupled systems and its broad applicability globally, we believe our model can become a central component of future estuarine management strategies. Recommendations are made for future improvements to the model design, increasing both its range of simulated ecological processes and the validity of its predictions.

year: 2022

title: An evaluation of Te Rau Puawai workforce 100: Evaluation overview

authors: Nikora, Linda Waimarie

subjects: Maori students

abstract: In July 2001, the Maori & Psychology Research Unit of the University of Waikato was asked to conduct an evaluation of the Te Rau Puawai programme, a joint venture between the former Health Funding Authority and Massey University. The overall goal of the programme is to contribute at least 100 Maori graduates to the Maori mental health workforce within a five year period. The overall aim of the evaluation was to provide the Ministry of Health with a clearer understanding of the programme including: the perceived critical success factors, the barriers if any regarding Te Rau Puawai, the impact of the programme, the extent to which the programme may be transferable, gaps in the programme, and suggested improvements. Through archival search, questionnaire surveys and interviews, evaluative data was collected from major stakeholders in the Te Rau Puawai programme.

text: An evaluation of Te Rau Puawai workforce 100: Evaluation overview In July 2001, the Maori & Psychology Research Unit of the University of Waikato was asked to conduct an evaluation of the Te Rau Puawai programme, a joint venture between the former Health Funding Authority and Massey University. The overall goal of the programme is to contribute at least 100 Maori graduates to the Maori mental health workforce within a five year period. The overall aim of the evaluation was to provide the Ministry of Health with a clearer understanding of the programme including: the perceived critical success factors, the barriers if any regarding Te Rau Puawai, the impact of the programme, the extent to which the programme may be transferable, gaps in the programme, and suggested improvements. Through archival search, questionnaire surveys and interviews, evaluative data was collected from major stakeholders in the Te Rau Puawai programme.

year: 2002-05-01