title: Rapid dissipation in a current sheet driven by footpoints motions

authors: Fruit, G.

subjects: Magnetohydrodynamics

abstract: Context.Wave energy dissipation by viscous and resistive damping in magnetic coronal plasmas is addressed. A two and one half dimensional, line-tied magnetic channel is considered whose footpoints are disturbed by buffeting motions of the photosphere.
Aims.The aim of the analysis is to determine how effectively shear Alfvén waves, driven by footpoint motions and resonating in the channel, can be damped by visco-resistive friction.
Methods.The problem is analyzed using a mixture of numerical and analytic techniques. Dynamic simulations, based on a cyclic footpoint driver, show that phase mixing resulting from variations in the magnetic field of the channel is instrumental in setting up a permanent "resonance regime" for the system. Analytic methods are used to analyze the resonance regime and to develop scaling laws for the rate of energy dissipation.
Results.We show that in the general case where the Alfvén velocity profile may be linearized around the resonance, the dissipation rate is "fast" in that it is not limited by small damping coefficients. Although large energies can accumulate within the channel in the limit of very small damping, we show that by tuning the driver to low frequencies, both the energy level and the dissipation rate can be made insensitive to the level of the damping.

text: Rapid dissipation in a current sheet driven by footpoints motions Context.Wave energy dissipation by viscous and resistive damping in magnetic coronal plasmas is addressed. A two and one half dimensional, line-tied magnetic channel is considered whose footpoints are disturbed by buffeting motions of the photosphere.
Aims.The aim of the analysis is to determine how effectively shear Alfvén waves, driven by footpoint motions and resonating in the channel, can be damped by visco-resistive friction.
Methods.The problem is analyzed using a mixture of numerical and analytic techniques. Dynamic simulations, based on a cyclic footpoint driver, show that phase mixing resulting from variations in the magnetic field of the channel is instrumental in setting up a permanent "resonance regime" for the system. Analytic methods are used to analyze the resonance regime and to develop scaling laws for the rate of energy dissipation.
Results.We show that in the general case where the Alfvén velocity profile may be linearized around the resonance, the dissipation rate is "fast" in that it is not limited by small damping coefficients. Although large energies can accumulate within the channel in the limit of very small damping, we show that by tuning the driver to low frequencies, both the energy level and the dissipation rate can be made insensitive to the level of the damping.

year: 2006

title: Yield of annealing on the properties of the Ti-5Al-2.5Fe alloy produced by Powder Forging

authors: Jia, Mingtu

abstract: The high cost of titanium alloys can be reduced using alternative manufacturing techniques and using cheap alloying elements. In this study, the Ti-5Al-2.5Fe alloy, a cheaper α + β alloy than the workhorse Ti-6Al-4V, was produced by powder metallurgy combined with hot thermomechanical deformation by means of forging. The forged alloy was subsequently subjected to a heat treatment at 750 °C for several annealing times in order to modify the microstructure and tailor the mechanical properties. This study demonstrates that, regardless of the forging temperature used, annealing of the forged Ti-5Al-2.5Fe alloy improves both the strength and the ductility. Generally, the longer the annealing time, the higher the gain in strength and ductility with respect to the forged alloy. Moreover, annealing is significantly more beneficial to improve the ductility rather than the strength of the powder-forged Ti-5Al-2.5Fe alloy.

text: Yield of annealing on the properties of the Ti-5Al-2.5Fe alloy produced by Powder Forging The high cost of titanium alloys can be reduced using alternative manufacturing techniques and using cheap alloying elements. In this study, the Ti-5Al-2.5Fe alloy, a cheaper α + β alloy than the workhorse Ti-6Al-4V, was produced by powder metallurgy combined with hot thermomechanical deformation by means of forging. The forged alloy was subsequently subjected to a heat treatment at 750 °C for several annealing times in order to modify the microstructure and tailor the mechanical properties. This study demonstrates that, regardless of the forging temperature used, annealing of the forged Ti-5Al-2.5Fe alloy improves both the strength and the ductility. Generally, the longer the annealing time, the higher the gain in strength and ductility with respect to the forged alloy. Moreover, annealing is significantly more beneficial to improve the ductility rather than the strength of the powder-forged Ti-5Al-2.5Fe alloy.

year: 2023

title: Te kawa whakauru ora: Transformative pathways to flourishing whānau

authors: Raharuhi, Te Urukeiha

subjects: flourishing whānau

abstract: Flourishing is more than a combination of wellbeing factors or the absence of disease. It is a state of vitality, optimism and potential. We flourish when we feel positive about our ability to make choices to improve our lives. We flourish when we have opportunities to make valuable contributions to those we care most about, in ways that are meaningful to us. 

There is a wealth of research about whānau wellbeing. However, it is difficult to discern how it directly benefits whānau. Furthermore, deficit approaches to whānau wellbeing research publicise negative stereotypes that are alienating for Māori and detrimental to our flourishing. Te Kawa Whakauru Ora explores a process of identifying transformative pathways to flourishing whānau. It is not a generic approach that represents whānau as homogenous. Nor does it equate whānau with household or nuclear family. This research inquiry into flourishing whānau occurs within the scope of whakapapa and explores diversity within my whānau. 

This research inquiry compares whānau participation in individual wellbeing activities with participation in whānau events. Whānau events are identified by whānau as the only occasions where we experience whakapapa, whanaungatanga and aspects of flourishing that are unique to our collective wellbeing. The research inquiry then focuses on trialling a process of identifying pathways to flourishing whānau through participation in whānau events. When we participate in whānau events, we simultaneously access many aspects of flourishing to varying degrees. Te reo Māori and Māori concepts that are accessible to all whānau regardless of our level of proficiency, are tools to raise our awareness about these. When coupled with an existing research framework, a process for time series analysis of flourishing whānau is created, allowing us to document and compare the contexts of flourishing experienced at different events. 

The trial process of identifying transformative pathways to flourishing whānau is described in detail throughout this thesis to engage with whānau wanting to document the contexts within which they access flourishing. The research process recognises that the potential for pathways to be transformative increases when these are identified by each whānau. This thesis is thus different from existing research about whānau wellbeing because it demonstrates and strengthens whānau research capability.

text: Te kawa whakauru ora: Transformative pathways to flourishing whānau Flourishing is more than a combination of wellbeing factors or the absence of disease. It is a state of vitality, optimism and potential. We flourish when we feel positive about our ability to make choices to improve our lives. We flourish when we have opportunities to make valuable contributions to those we care most about, in ways that are meaningful to us. 

There is a wealth of research about whānau wellbeing. However, it is difficult to discern how it directly benefits whānau. Furthermore, deficit approaches to whānau wellbeing research publicise negative stereotypes that are alienating for Māori and detrimental to our flourishing. Te Kawa Whakauru Ora explores a process of identifying transformative pathways to flourishing whānau. It is not a generic approach that represents whānau as homogenous. Nor does it equate whānau with household or nuclear family. This research inquiry into flourishing whānau occurs within the scope of whakapapa and explores diversity within my whānau. 

This research inquiry compares whānau participation in individual wellbeing activities with participation in whānau events. Whānau events are identified by whānau as the only occasions where we experience whakapapa, whanaungatanga and aspects of flourishing that are unique to our collective wellbeing. The research inquiry then focuses on trialling a process of identifying pathways to flourishing whānau through participation in whānau events. When we participate in whānau events, we simultaneously access many aspects of flourishing to varying degrees. Te reo Māori and Māori concepts that are accessible to all whānau regardless of our level of proficiency, are tools to raise our awareness about these. When coupled with an existing research framework, a process for time series analysis of flourishing whānau is created, allowing us to document and compare the contexts of flourishing experienced at different events. 

The trial process of identifying transformative pathways to flourishing whānau is described in detail throughout this thesis to engage with whānau wanting to document the contexts within which they access flourishing. The research process recognises that the potential for pathways to be transformative increases when these are identified by each whānau. This thesis is thus different from existing research about whānau wellbeing because it demonstrates and strengthens whānau research capability.

year: 2025