title: Influence of porosity on mechanical behaviour and gas permeability of Ti compacts prepared by slip casting

authors: Xu, Qian

subjects: porous materials

abstract: Porous titanium compacts with porosity in the range of 12.3–35.3 vol% were fabricated by slip casting. Slip casting is emerging to be an attractive process for fabrication of porous titanium products. The mechanical properties, fracture morphology, gas permeability, pore size analysis and pore shape factors for the porous Ti compacts were determined for different porosity levels. A decreasing porosity level resulted in less open porosity and gas permeability, reduced pore size, and an increased tensile stress and elongation. The mechanical properties of porous titanium compacts produced by slip casting were comparable with more conventional press and sintered materials at the same porosity levels. Theoretical models for tensile stress and ductility as a function of porosity were examined and incorporated into the results and differences between the theoretical models and experimental results are discussed. The pore shape factor analysis showed that tensile loading would stretch the pores in the compacts to produce more irregular pores, which were acting as linkage sites to allow the propagation of cracks. Additionally, a novel interconnected pore characterisation method using ammonium meta-tungstate solution is presented. By using backscatter scanning electron microscopy, the interconnected pores can be directly observed.

text: Influence of porosity on mechanical behaviour and gas permeability of Ti compacts prepared by slip casting Porous titanium compacts with porosity in the range of 12.3–35.3 vol% were fabricated by slip casting. Slip casting is emerging to be an attractive process for fabrication of porous titanium products. The mechanical properties, fracture morphology, gas permeability, pore size analysis and pore shape factors for the porous Ti compacts were determined for different porosity levels. A decreasing porosity level resulted in less open porosity and gas permeability, reduced pore size, and an increased tensile stress and elongation. The mechanical properties of porous titanium compacts produced by slip casting were comparable with more conventional press and sintered materials at the same porosity levels. Theoretical models for tensile stress and ductility as a function of porosity were examined and incorporated into the results and differences between the theoretical models and experimental results are discussed. The pore shape factor analysis showed that tensile loading would stretch the pores in the compacts to produce more irregular pores, which were acting as linkage sites to allow the propagation of cracks. Additionally, a novel interconnected pore characterisation method using ammonium meta-tungstate solution is presented. By using backscatter scanning electron microscopy, the interconnected pores can be directly observed.

year: 2013-12

title: Generalised Nonblocking

authors: Malik, Robi

subjects: computer science

abstract: This paper studies the nonblocking check used in supervisory control of discrete event systems and its limitations. Different examples with different liveness requirements are discussed. It is shown that the standard nonblocking check can be used to specify most requirements of interest, but that it lacks expressive power in a few cases. A generalised nonblocking check is proposed to overcome the weakness, and its relationship to standard nonblocking is explored. Results suggest that generalised nonblocking, while having the same useful properties with respect to synthesis and compositional verification, can provide for more concise problem representations in some cases.

text: Generalised Nonblocking This paper studies the nonblocking check used in supervisory control of discrete event systems and its limitations. Different examples with different liveness requirements are discussed. It is shown that the standard nonblocking check can be used to specify most requirements of interest, but that it lacks expressive power in a few cases. A generalised nonblocking check is proposed to overcome the weakness, and its relationship to standard nonblocking is explored. Results suggest that generalised nonblocking, while having the same useful properties with respect to synthesis and compositional verification, can provide for more concise problem representations in some cases.

year: 2008

title: Science-practice roadshow 1: Summary perspectives from centralised entities and agencies

authors: Serrao-Neumann, Silvia

abstract: Flooding is Aotearoa-New Zealand’s most frequent natural hazard, regularly damaging buildings and infrastructure networks, and causing months of disruption to communities and businesses (Hutchings et al. 2019). Also, floods have indirect, cascading, and more intangible impacts (Lawrence, Blackett, and Cradock-Henry 2020), such as the withdrawal of future investment or the emotional stress of recovery. flood risk is predicted to rise quickly due to the combination of climate change and rapid urban intensification (Ministry for the Environment and The Flood Risk Management and River Control Review Steering Group 2008). 

Currently, there is no consistent approach to accurately determine flood risk on a national scale, nor how this may be changing as the climate warms. Instead, flooding risk assessments are done for individual catchments or locations, with the goal of managing and mitigating on the local scale. Local and regional governments vary widely in their capability and capacity to undertake this work (Ford, Berrang-Ford, and Berrang Ford 2011) and, thus, significant differences in data availability and modelling approaches mean that integration of results to gain a pan-region or nationwide picture has not been possible. 

The ‘Mā te haumaru ō nga puna wai ō Rākaihautū ka ora mo ake tonu: Increasing flood resilience across Aotearoa’ research develop a detailed nationwide model that could inform strategic and co-ordinated nationwide decision-making and regulations to support improved resilience to flood risk across the country. Utilising new methods and advances in computer processing and automation, the programme is developing a dynamic risk modelling framework that will assess flood hazard for every catchment in the country and under differing climate scenarios. The model will account for the risks to both built infrastructure and communities so that a fuller understanding of societal costs and impacts can be established. The model’s utility for supporting decision-making will be investigated using an initial set of scenarios for environmental planning, policy settings and infrastructure investment options. Two overarching themes across all of the research - Mtauranga Mori and Uncertainty – are designed to utilise the diverse knowledge systems available to develop tools that are relevant for communities throughout Aotearoa-New Zealand, and to take into account and communicate more clearly flood risks. 

Improved resilience to flooding across Aotearoa-New Zealand is a key outcome sought by the research programme, however it cannot be achieved by research alone. Instead, knowledge and information developed within the programme must be utilised by practitioners in their work to assist communities to plan for, manage, mitigate and avoid flood risks. New knowledge from the programme must be incorporated by practitioners into further tools, policy and decision-making frameworks. This knowledge translation however is not a straight forward process (Dilling and Lemos 2011). Cultural, behavioural and cognitive differences between those who produce and those who utilise knowledge mean that research outputs may not fit the requirements of their intended users, and thus, uptake of research outputs may be compromised. Conversely, strong engagement of knowledge users in the knowledge production process is known to increase the likelihood, and impact, of knowledge implementation. 

Stakeholders are key members of the programme’s research team, representing views across central and local government, engineering, planning consultancies, emergency management, insurance and banking industries, and Te Rūnanga o Wairewa (Banks Peninsula). To broaden the range of stakeholder perspectives, and to facilitate relationships across the programme, we have established a boundary organisation – Te W Te W . Boundary organisations (Guston 2001; Kirchhoff, Esselman, and Brown 2015) are forums that bridge between the two relatively different social worlds of knowledge producers (researchers/scientists) and users (practitioners/policy makers). These forums create and sustain legitimate space and collaboration for knowledge/information to be co-designed, co-produced and co-disseminated (Serrao-Neumann, Di Giulio, and Low Choy 2020). Within our programme, Te W Te W is responsible for organising and facilitating communication and collaboration activities – events (Science-Practice oadshows), communications channels such as an electronic newsletter and website, and learning opportunities. Through this organisation, we are fostering trust, legitimacy and capacity for information use so that our research results will be usable, useful, and used. 

This report summarises the discussion and perspectives shared at the first Science-Practice Roadshow held in October 2021.

text: Science-practice roadshow 1: Summary perspectives from centralised entities and agencies Flooding is Aotearoa-New Zealand’s most frequent natural hazard, regularly damaging buildings and infrastructure networks, and causing months of disruption to communities and businesses (Hutchings et al. 2019). Also, floods have indirect, cascading, and more intangible impacts (Lawrence, Blackett, and Cradock-Henry 2020), such as the withdrawal of future investment or the emotional stress of recovery. flood risk is predicted to rise quickly due to the combination of climate change and rapid urban intensification (Ministry for the Environment and The Flood Risk Management and River Control Review Steering Group 2008). 

Currently, there is no consistent approach to accurately determine flood risk on a national scale, nor how this may be changing as the climate warms. Instead, flooding risk assessments are done for individual catchments or locations, with the goal of managing and mitigating on the local scale. Local and regional governments vary widely in their capability and capacity to undertake this work (Ford, Berrang-Ford, and Berrang Ford 2011) and, thus, significant differences in data availability and modelling approaches mean that integration of results to gain a pan-region or nationwide picture has not been possible. 

The ‘Mā te haumaru ō nga puna wai ō Rākaihautū ka ora mo ake tonu: Increasing flood resilience across Aotearoa’ research develop a detailed nationwide model that could inform strategic and co-ordinated nationwide decision-making and regulations to support improved resilience to flood risk across the country. Utilising new methods and advances in computer processing and automation, the programme is developing a dynamic risk modelling framework that will assess flood hazard for every catchment in the country and under differing climate scenarios. The model will account for the risks to both built infrastructure and communities so that a fuller understanding of societal costs and impacts can be established. The model’s utility for supporting decision-making will be investigated using an initial set of scenarios for environmental planning, policy settings and infrastructure investment options. Two overarching themes across all of the research - Mtauranga Mori and Uncertainty – are designed to utilise the diverse knowledge systems available to develop tools that are relevant for communities throughout Aotearoa-New Zealand, and to take into account and communicate more clearly flood risks. 

Improved resilience to flooding across Aotearoa-New Zealand is a key outcome sought by the research programme, however it cannot be achieved by research alone. Instead, knowledge and information developed within the programme must be utilised by practitioners in their work to assist communities to plan for, manage, mitigate and avoid flood risks. New knowledge from the programme must be incorporated by practitioners into further tools, policy and decision-making frameworks. This knowledge translation however is not a straight forward process (Dilling and Lemos 2011). Cultural, behavioural and cognitive differences between those who produce and those who utilise knowledge mean that research outputs may not fit the requirements of their intended users, and thus, uptake of research outputs may be compromised. Conversely, strong engagement of knowledge users in the knowledge production process is known to increase the likelihood, and impact, of knowledge implementation. 

Stakeholders are key members of the programme’s research team, representing views across central and local government, engineering, planning consultancies, emergency management, insurance and banking industries, and Te Rūnanga o Wairewa (Banks Peninsula). To broaden the range of stakeholder perspectives, and to facilitate relationships across the programme, we have established a boundary organisation – Te W Te W . Boundary organisations (Guston 2001; Kirchhoff, Esselman, and Brown 2015) are forums that bridge between the two relatively different social worlds of knowledge producers (researchers/scientists) and users (practitioners/policy makers). These forums create and sustain legitimate space and collaboration for knowledge/information to be co-designed, co-produced and co-disseminated (Serrao-Neumann, Di Giulio, and Low Choy 2020). Within our programme, Te W Te W is responsible for organising and facilitating communication and collaboration activities – events (Science-Practice oadshows), communications channels such as an electronic newsletter and website, and learning opportunities. Through this organisation, we are fostering trust, legitimacy and capacity for information use so that our research results will be usable, useful, and used. 

This report summarises the discussion and perspectives shared at the first Science-Practice Roadshow held in October 2021.

year: 2022-02