title: Optimal task scheduling in a flexible manufacturing system using model checking

authors: Malik, Robi

subjects: computer science

abstract: This paper demonstrates the use of model checking to solve the problem of optimal task scheduling in a flexible manufacturing system. The system is modelled as a discrete event system, for which the least restrictive safe behaviour is synthesised according to supervisory control theory. Then timing constraints are added to the model in the form of extended finitestate machines, and time-optimal schedules are computed using the discrete event systems and model checking tool Supremica. In the case study considered in this paper, which previously was only solved heuristically, the method successfully produces optimal schedules to manufacture up to 30 products of two different types. The method is furthermore used to find an optimal cycle, solving the scheduling problem of the case study for an arbitrary number of products in optimal or asymptotically close to optimal time.

text: Optimal task scheduling in a flexible manufacturing system using model checking This paper demonstrates the use of model checking to solve the problem of optimal task scheduling in a flexible manufacturing system. The system is modelled as a discrete event system, for which the least restrictive safe behaviour is synthesised according to supervisory control theory. Then timing constraints are added to the model in the form of extended finitestate machines, and time-optimal schedules are computed using the discrete event systems and model checking tool Supremica. In the case study considered in this paper, which previously was only solved heuristically, the method successfully produces optimal schedules to manufacture up to 30 products of two different types. The method is furthermore used to find an optimal cycle, solving the scheduling problem of the case study for an arbitrary number of products in optimal or asymptotically close to optimal time.

year: 2018

title: Identifying dissolved oxygen variability and stress in tidal freshwater streams of northern New Zealand

authors: Wilding, Thomas K.

subjects: dissolved oxygen

abstract: Tidal streams are ecologically important components of lotic network, and we identify dissolved oxygen (DO) depletion as a potentially important stressor in freshwater tidal streams of northern New Zealand. Other studies have examined temporal DO variability within rivers and we build on this by examining variability between streams as a basis for regional-scale predictors of risk for DO stress. Diel DO variability in these streams was driven by: (1) photosynthesis by aquatic plants and community respiration which produced DO maxima in the afternoon and minima early morning (range, 0.6–4.7 g/m³) as a product of the solar cycle and (2) tidal variability as a product of the lunar cycle, including saline intrusions with variable DO concentrations plus a small residual effect on freshwater DO for low-velocity streams. The lowest DO concentrations were observed during March (early autumn) when water temperatures and macrophyte biomass were high. Spatial comparisons indicated that lowgradient tidal streams were at greater risk of DO depletions harmful to aquatic life. Tidal influence was stronger in low-gradient streams, which typically drain more developed catchments, have lower reaeration potential and offer conditions more suitable for aquatic plant proliferation. Combined, these characteristics supported a simple method based on the extent of low-gradient channel for identifying coastal streams at risk of DO depletion. High-risk streams can then be targeted for riparian planting, nutrient limits and water allocation controls to reduce potential ecological stress.

text: Identifying dissolved oxygen variability and stress in tidal freshwater streams of northern New Zealand Tidal streams are ecologically important components of lotic network, and we identify dissolved oxygen (DO) depletion as a potentially important stressor in freshwater tidal streams of northern New Zealand. Other studies have examined temporal DO variability within rivers and we build on this by examining variability between streams as a basis for regional-scale predictors of risk for DO stress. Diel DO variability in these streams was driven by: (1) photosynthesis by aquatic plants and community respiration which produced DO maxima in the afternoon and minima early morning (range, 0.6–4.7 g/m³) as a product of the solar cycle and (2) tidal variability as a product of the lunar cycle, including saline intrusions with variable DO concentrations plus a small residual effect on freshwater DO for low-velocity streams. The lowest DO concentrations were observed during March (early autumn) when water temperatures and macrophyte biomass were high. Spatial comparisons indicated that lowgradient tidal streams were at greater risk of DO depletions harmful to aquatic life. Tidal influence was stronger in low-gradient streams, which typically drain more developed catchments, have lower reaeration potential and offer conditions more suitable for aquatic plant proliferation. Combined, these characteristics supported a simple method based on the extent of low-gradient channel for identifying coastal streams at risk of DO depletion. High-risk streams can then be targeted for riparian planting, nutrient limits and water allocation controls to reduce potential ecological stress.

year: 2012

title: Ngā whakaaro o ngā ākonga: perspectives and experiences of Māori students in outdoor education in Aotearoa New Zealand

authors: Washbourn, Phil

subjects: Outdoor education

abstract: This study aims to develop an understanding of the perspectives and experiences of Māori students in a secondary school outdoor education programme in Aotearoa New Zealand. Lynch (2012) indicated that “there is a clear need, and wide scope, for research into: cultural elements of outdoor education programmes; cultural effects on participants; culturally appropriate research approaches and programme effects on, and experiences of, people who identify as Māori” (p.49). Outdoor education in Aotearoa New Zealand has been heavily influenced by ‘Eurocentric’ values and practices that contrast with those of Te Ao Māori. In line with a number of calls to re-envision the field, the perspectives and experiences of Māori and the incorporation of Te Ao Māori pedagogies are vital to the reconstruction of an integrated and inclusive Aotearoa New Zealand expression of Outdoor Education for the 21st century.
This study, guided by culturally responsive research methodology, used focus groups to investigate the opinions, thoughts and expectations of Māori students of outdoor education. Thematic analysis was used to analyse the focus group data, and four major themes were identified: the importance of shared experience and relationships to positive experiences of outdoor education; the distinctive practices of outdoor education make learning enjoyable and engaging; the importance to students of making connections with Te Ao Māori through experience, stories of places and history; and the complexity of engaging Māori in participation in outdoor education, including factors such as affordability, the influence of friends and whānau and prioritising educational pathways. A range of practices and approaches from Te Ao Māori are considered and presented, based on the contribution of the student participants, including pedagogical principles from Te Ao Māori such as wānanga, whanaungatanga and tauira. Suggestions for practice include developing connections within the community and experiencing Te Ao Māori learning contexts such as waka ama, noho marae and mahinga kai.

text: Ngā whakaaro o ngā ākonga: perspectives and experiences of Māori students in outdoor education in Aotearoa New Zealand This study aims to develop an understanding of the perspectives and experiences of Māori students in a secondary school outdoor education programme in Aotearoa New Zealand. Lynch (2012) indicated that “there is a clear need, and wide scope, for research into: cultural elements of outdoor education programmes; cultural effects on participants; culturally appropriate research approaches and programme effects on, and experiences of, people who identify as Māori” (p.49). Outdoor education in Aotearoa New Zealand has been heavily influenced by ‘Eurocentric’ values and practices that contrast with those of Te Ao Māori. In line with a number of calls to re-envision the field, the perspectives and experiences of Māori and the incorporation of Te Ao Māori pedagogies are vital to the reconstruction of an integrated and inclusive Aotearoa New Zealand expression of Outdoor Education for the 21st century.
This study, guided by culturally responsive research methodology, used focus groups to investigate the opinions, thoughts and expectations of Māori students of outdoor education. Thematic analysis was used to analyse the focus group data, and four major themes were identified: the importance of shared experience and relationships to positive experiences of outdoor education; the distinctive practices of outdoor education make learning enjoyable and engaging; the importance to students of making connections with Te Ao Māori through experience, stories of places and history; and the complexity of engaging Māori in participation in outdoor education, including factors such as affordability, the influence of friends and whānau and prioritising educational pathways. A range of practices and approaches from Te Ao Māori are considered and presented, based on the contribution of the student participants, including pedagogical principles from Te Ao Māori such as wānanga, whanaungatanga and tauira. Suggestions for practice include developing connections within the community and experiencing Te Ao Māori learning contexts such as waka ama, noho marae and mahinga kai.

year: 2018