title: Ion parallel viscosity and anisotropy in MHD turbulence

authors: Oughton, Sean

subjects: magnetohydrodynamics (MHD)

abstract: We report on results from direct numerical simulation of the incompressible three- dimensional magnetohydrodynamic (MHD) equations, modified to incorporate viscous dissipation via the strongly anisotropic ion-parallel viscosity term. Both linear and nonlinear cases are considered, all with a strong background magnetic field. It is found that spectral anisotropy develops in almost all cases, but that the contribution from effects associated with the ion-parallel viscosity is relatively weak compared with the previously reported nonlinear process. Furthermore, and in contrast to this earlier work, it is suggested that when B₀ is large, the anisotropy will develop and persist for many large-scale turnover times even for non-dissipative runs. Resistive dissipation is found to dominate over viscous even when the resistivity is several orders of magnitude smaller than the ion parallel viscosity. A variance anisotropy effect and anisotropy dependence on the polarization of the fluctuations are also observed.

text: Ion parallel viscosity and anisotropy in MHD turbulence We report on results from direct numerical simulation of the incompressible three- dimensional magnetohydrodynamic (MHD) equations, modified to incorporate viscous dissipation via the strongly anisotropic ion-parallel viscosity term. Both linear and nonlinear cases are considered, all with a strong background magnetic field. It is found that spectral anisotropy develops in almost all cases, but that the contribution from effects associated with the ion-parallel viscosity is relatively weak compared with the previously reported nonlinear process. Furthermore, and in contrast to this earlier work, it is suggested that when B₀ is large, the anisotropy will develop and persist for many large-scale turnover times even for non-dissipative runs. Resistive dissipation is found to dominate over viscous even when the resistivity is several orders of magnitude smaller than the ion parallel viscosity. A variance anisotropy effect and anisotropy dependence on the polarization of the fluctuations are also observed.

year: 1996

title: Synthesis, characterisation, and properties of powder metallurgy transition metal-based high entropy alloys for electrocatalytic application

authors: Kumar, Ashok

subjects: Powder metallurgy

abstract: Water electrolysis is an eco-friendly route for hydrogen production when compared to other routes such as steam reforming, coal gasification, biomass gasification etc, however only 4% of hydrogen is being produced through water electrolysis. Water electrolysis proceeds via two half-cell reactions namely oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). HER is a two-electron transfer process while OER is a four electron/proton transfer process. Hence OER is energy intensive and affects the overall efficiency of water electrolysis. To improve the efficiency of water electrolysis, it is necessary to develop an efficient electrocatalyst for OER process. Ir and Ru based oxides are the state-of-the-art electrocatalysts for OER, however their natural abundance is minuscule, hence they are expensive. Transition metal based electrocatalysts are emerging materials for OER applications due to their high natural abundance and low cost. However, these materials exhibit poor conductivity and consequently poor catalytic activity. Hence to overcome the shortcomings of conventional electrocatalysts a new class of multi component alloys termed as high entropy alloys (HEAs) are getting popular for electrocatalytic applications. However, most of the HEAs for OER are not self-supporting and being synthesised in powder form are often coated onto conductive substrates such as Ni foam and carbon fibre. Hence this powder based electrocatalysts are not suitable for industrial scale hydrogen production. In addition, most synthesised HEAs consist of Co which is an inherently expensive material. To overcome these current drawbacks in this field, this thesis considered three Co free self-supporting HEA combinations namely NiMnFeCu, NiMnFeCrCu and NiMnFeCr which were successfully synthesized. Among the synthesized HEAs examined, NiMnFeCr was found to exhibit an overpotential of 300 mV after it was subjected to 100 cycles of cyclic voltammetry (CV) activation. Furthermore, the NiMnFeCr HEA synthesised exhibited a compressive yield stress of 306 MPa manifesting the excellent combined properties of not only catalytic activity but also mechanical strength. The research showed that NiMnFeCr was a suitable candidate material for industrial scale water electrolysis and hence can be considered as a potential replacement for the conventional, prominently used electrocatalysts such as Raney nickel, Ir and Ru oxide- based catalysts. The excellent catalytic activity demonstrated by the HEA NiMnFeCr could also be attributed to its work function of 3.02 eV which is the lowest value of work function of other studied HEAs.

text: Synthesis, characterisation, and properties of powder metallurgy transition metal-based high entropy alloys for electrocatalytic application Water electrolysis is an eco-friendly route for hydrogen production when compared to other routes such as steam reforming, coal gasification, biomass gasification etc, however only 4% of hydrogen is being produced through water electrolysis. Water electrolysis proceeds via two half-cell reactions namely oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). HER is a two-electron transfer process while OER is a four electron/proton transfer process. Hence OER is energy intensive and affects the overall efficiency of water electrolysis. To improve the efficiency of water electrolysis, it is necessary to develop an efficient electrocatalyst for OER process. Ir and Ru based oxides are the state-of-the-art electrocatalysts for OER, however their natural abundance is minuscule, hence they are expensive. Transition metal based electrocatalysts are emerging materials for OER applications due to their high natural abundance and low cost. However, these materials exhibit poor conductivity and consequently poor catalytic activity. Hence to overcome the shortcomings of conventional electrocatalysts a new class of multi component alloys termed as high entropy alloys (HEAs) are getting popular for electrocatalytic applications. However, most of the HEAs for OER are not self-supporting and being synthesised in powder form are often coated onto conductive substrates such as Ni foam and carbon fibre. Hence this powder based electrocatalysts are not suitable for industrial scale hydrogen production. In addition, most synthesised HEAs consist of Co which is an inherently expensive material. To overcome these current drawbacks in this field, this thesis considered three Co free self-supporting HEA combinations namely NiMnFeCu, NiMnFeCrCu and NiMnFeCr which were successfully synthesized. Among the synthesized HEAs examined, NiMnFeCr was found to exhibit an overpotential of 300 mV after it was subjected to 100 cycles of cyclic voltammetry (CV) activation. Furthermore, the NiMnFeCr HEA synthesised exhibited a compressive yield stress of 306 MPa manifesting the excellent combined properties of not only catalytic activity but also mechanical strength. The research showed that NiMnFeCr was a suitable candidate material for industrial scale water electrolysis and hence can be considered as a potential replacement for the conventional, prominently used electrocatalysts such as Raney nickel, Ir and Ru oxide- based catalysts. The excellent catalytic activity demonstrated by the HEA NiMnFeCr could also be attributed to its work function of 3.02 eV which is the lowest value of work function of other studied HEAs.

year: 2023

title: Developing a kaupapa Māori evaluation model – one size fits all?

authors: Masters-Awatere, Bridgette

subjects: Maori health

abstract: Health statistics in Aotearoa (New Zealand) highlight that Māori, the indigenous people Aotearoa have poorer health than non- Māori. In response to the statistics a number of Māori health providers have established services that address specific areas of need in their regions. Initially there were minimal accountability requirements of providers. However, changes in the health system now mean that groups wanting to establish a new service must provide accountability measures before, during and after the funding has been allocated. As a result providers need to develop a rationale behind their decisions and assess the measure of change that has taken place as a result of the service or programme to ensure continued funding. The requirements reflect the dominant Western paradigm in which health promotion is understood to be about producing specific quantifiable behaviour changes in individuals. Māori health providers on the other hand have tended to take a holistic approach to health. Thus they have found themselves in the position of trying to show change within a paradigm where measurements are not easily taken. This has created frustration amongst Māori providers who face losing their funding because of an inability to report measurable outcomes using a framework that does not apply to their culture.

text: Developing a kaupapa Māori evaluation model – one size fits all? Health statistics in Aotearoa (New Zealand) highlight that Māori, the indigenous people Aotearoa have poorer health than non- Māori. In response to the statistics a number of Māori health providers have established services that address specific areas of need in their regions. Initially there were minimal accountability requirements of providers. However, changes in the health system now mean that groups wanting to establish a new service must provide accountability measures before, during and after the funding has been allocated. As a result providers need to develop a rationale behind their decisions and assess the measure of change that has taken place as a result of the service or programme to ensure continued funding. The requirements reflect the dominant Western paradigm in which health promotion is understood to be about producing specific quantifiable behaviour changes in individuals. Māori health providers on the other hand have tended to take a holistic approach to health. Thus they have found themselves in the position of trying to show change within a paradigm where measurements are not easily taken. This has created frustration amongst Māori providers who face losing their funding because of an inability to report measurable outcomes using a framework that does not apply to their culture.

year: 2002