title: Factors controlling the tensile properties of ultrafine structured Cu–5vol%Al₂O₃ nanocomposite prepared by high energy mechanical milling and powder compact extrusion

authors: Zhou, Dengshan

subjects: high energy mechanical milling

abstract: The microstructures and tensile properties of two ultrafine structured Cu–5vol%Al₂O₃ nanocomposite samples made by a combination of high energy mechanical milling of a mixture of Cu powder and gamma Al₂O₃ nanopowder and powder compact extrusion were studied. The sample extruded at 750 °C exhibited a microstructure consisting of Cu grains with sizes in the range of 100–500 nm and a dispersion of Al₂O₃ nanoparticles with sizes in the range of 20–345 nm. With the extrusion temperature increasing to 900 °C, the Cu grain sizes remained almost unchanged, but a large fraction of the Al₂O₃ nanoparticles were dissolved, leading to possible formation of nanometer sized Al³⁺/O²⁻ clusters. This microstructural difference of the two samples causes an interesting difference in tensile properties, with the sample extruded at 900 °C showing approximately 150 MPa higher yield strength and ultimate tensile strength and also better ductility than the sample extruded at 750 °C. It appears that this significant beneficial effect of dissolution of Al₂O₃ nanoparticles is mainly caused by the significant strengthening effect of the nanometer sized Al³⁺/O²⁻ clusters through Orowan mechanism.

text: Factors controlling the tensile properties of ultrafine structured Cu–5vol%Al₂O₃ nanocomposite prepared by high energy mechanical milling and powder compact extrusion The microstructures and tensile properties of two ultrafine structured Cu–5vol%Al₂O₃ nanocomposite samples made by a combination of high energy mechanical milling of a mixture of Cu powder and gamma Al₂O₃ nanopowder and powder compact extrusion were studied. The sample extruded at 750 °C exhibited a microstructure consisting of Cu grains with sizes in the range of 100–500 nm and a dispersion of Al₂O₃ nanoparticles with sizes in the range of 20–345 nm. With the extrusion temperature increasing to 900 °C, the Cu grain sizes remained almost unchanged, but a large fraction of the Al₂O₃ nanoparticles were dissolved, leading to possible formation of nanometer sized Al³⁺/O²⁻ clusters. This microstructural difference of the two samples causes an interesting difference in tensile properties, with the sample extruded at 900 °C showing approximately 150 MPa higher yield strength and ultimate tensile strength and also better ductility than the sample extruded at 750 °C. It appears that this significant beneficial effect of dissolution of Al₂O₃ nanoparticles is mainly caused by the significant strengthening effect of the nanometer sized Al³⁺/O²⁻ clusters through Orowan mechanism.

year: 2013

title: Mixed basis matrix elements for the subgroup reductions of SO(2,1)

authors: Kalnins, Ernie G.

subjects: Mathematics

abstract: By using the irreducible decomposition on the two-dimensional light cone, the mixed basis matrix elements for the three subgroup reductions of SO(2,1) are calculated. These matrix elements are calculated for the principal series only and can be expressed in terms of well-known special functions. As a consequence of appearing in this context, some new properties of these special functions are given.

text: Mixed basis matrix elements for the subgroup reductions of SO(2,1) By using the irreducible decomposition on the two-dimensional light cone, the mixed basis matrix elements for the three subgroup reductions of SO(2,1) are calculated. These matrix elements are calculated for the principal series only and can be expressed in terms of well-known special functions. As a consequence of appearing in this context, some new properties of these special functions are given.

year: 1973-05

title: Taking Taniwha seriously

authors: Kingsbury, Justine

subjects: intercultural understanding

abstract: Taniwha are powerful water creatures in te ao Māori (the Māori world/worldview). Taniwha sometimes afect public works in Aotearoa New Zealand: for example, consultation between government agencies and tangata whenua (the people of the land) about proposed roading developments sometimes results in the route being moved to avoid the dwelling place of a taniwha. Mainstream media responses have tended to be hostile or mocking, as you might expect, since on the face of it the dominant western scientifc worldview has no place for beings like taniwha. However, in the 2020s, there appears to be an increased willingness to engage with te ao Māori. In this spirit, this paper proposes a way for non-Māori to begin to take taniwha more seriously, taking as its starting point the work of Dan Hikuroa on the practical usefulness of taniwha pūrākau (traditional narratives) in encoding information about natural hazards. The focus of this paper is narrow, but aspects of the strategy it proposes may be generalisable both to other aspects of te ao Māori and to other bicultural and multicultural contexts.

text: Taking Taniwha seriously Taniwha are powerful water creatures in te ao Māori (the Māori world/worldview). Taniwha sometimes afect public works in Aotearoa New Zealand: for example, consultation between government agencies and tangata whenua (the people of the land) about proposed roading developments sometimes results in the route being moved to avoid the dwelling place of a taniwha. Mainstream media responses have tended to be hostile or mocking, as you might expect, since on the face of it the dominant western scientifc worldview has no place for beings like taniwha. However, in the 2020s, there appears to be an increased willingness to engage with te ao Māori. In this spirit, this paper proposes a way for non-Māori to begin to take taniwha more seriously, taking as its starting point the work of Dan Hikuroa on the practical usefulness of taniwha pūrākau (traditional narratives) in encoding information about natural hazards. The focus of this paper is narrow, but aspects of the strategy it proposes may be generalisable both to other aspects of te ao Māori and to other bicultural and multicultural contexts.

year: 2022-11-10