title: Characterizing the mechanical properties of fused deposition modelling natural fiber recycled polypropylene composites

authors: Milosevic, M.

abstract: The objective of this investigation was to characterize the performance of natural fiber reinforced polypropylene composites in fused deposition modelling (FDM). Composite filaments comprising of pre-consumer recycled polypropylene with varying contents of hemp or harakeke fibers were extruded from which tensile test specimens were made using FDM. Filament and test specimens were tensile tested and properties were compared with plain polypropylene samples; the ultimate tensile strength and Young’s modulus of reinforced filament increased by more than 50% and 143%, respectively, for both 30 wt % hemp or harakeke compared to polypropylene filament. However, the same degree of improvement was not seen with the FDM test specimens, with several compositions having properties lower than for unfilled polypropylene. SEM analysis of fracture surfaces revealed uniform fiber dispersion and reasonable fiber alignment, but porosity and fiber pull-out were also observed. Fiber reinforcement was found to give benefit regarding dimensional stability during extrusion and FDM, which is of major importance for its implementation in FDM. Recommendations for optimization of processing in order to enhance build quality and improve mechanical properties are provided.

text: Characterizing the mechanical properties of fused deposition modelling natural fiber recycled polypropylene composites The objective of this investigation was to characterize the performance of natural fiber reinforced polypropylene composites in fused deposition modelling (FDM). Composite filaments comprising of pre-consumer recycled polypropylene with varying contents of hemp or harakeke fibers were extruded from which tensile test specimens were made using FDM. Filament and test specimens were tensile tested and properties were compared with plain polypropylene samples; the ultimate tensile strength and Young’s modulus of reinforced filament increased by more than 50% and 143%, respectively, for both 30 wt % hemp or harakeke compared to polypropylene filament. However, the same degree of improvement was not seen with the FDM test specimens, with several compositions having properties lower than for unfilled polypropylene. SEM analysis of fracture surfaces revealed uniform fiber dispersion and reasonable fiber alignment, but porosity and fiber pull-out were also observed. Fiber reinforcement was found to give benefit regarding dimensional stability during extrusion and FDM, which is of major importance for its implementation in FDM. Recommendations for optimization of processing in order to enhance build quality and improve mechanical properties are provided.

year: 2017

title: Measurement of implant electrode leads using time-domain reflectometry to predict the resonant length for MRI heating

authors: McCabe, Steven Owen

abstract: Magnetic Resonance Imaging (MRI) machines can generate hazardous RF heating of patients with implanted neurostimulation leads. Consequently, most patients with these implants are contraindicated from having MRI scans. The level of RF heating has a strong dependence on lead length and is most severe when the length is close to a specific resonant length. Recent studies have shown that simple modifications to the lead construction and insulating material can alter the resonant length and significantly ameliorate this heating hazard, achieving MRI safety. We propose a technique using time domain reflectometry (TDR) to find the resonant length of an arbitrary lead such to minimise the amount of MRI machine time needed to find the length of highest heating. The results are compared with temperature measurements made in a 3-Tesla MRI machine and with a CW dipole radiator in the lab.

text: Measurement of implant electrode leads using time-domain reflectometry to predict the resonant length for MRI heating Magnetic Resonance Imaging (MRI) machines can generate hazardous RF heating of patients with implanted neurostimulation leads. Consequently, most patients with these implants are contraindicated from having MRI scans. The level of RF heating has a strong dependence on lead length and is most severe when the length is close to a specific resonant length. Recent studies have shown that simple modifications to the lead construction and insulating material can alter the resonant length and significantly ameliorate this heating hazard, achieving MRI safety. We propose a technique using time domain reflectometry (TDR) to find the resonant length of an arbitrary lead such to minimise the amount of MRI machine time needed to find the length of highest heating. The results are compared with temperature measurements made in a 3-Tesla MRI machine and with a CW dipole radiator in the lab.

year: 2016

title: Street-level bureaucracy and occupational therapy practices in Aotearoa New Zealand. A genealogical critique.

authors: Silcock, Elizabeth Mary

subjects: power

abstract: As a human science that is also part of administering and supporting bureaucracy, occupational therapy functions in multi-layered networks of power  that support many different social structures. Occupational therapists’ work often involves operationalising health, education and social services at the street-level, positioning them between the aspirations of both policy and social activism and material life outcomes. Through a genealogical critique, this thesis problematises the practice of occupational therapy through a Foucauldian lens that views everything as dangerous. By viewing occupational therapy practice as dangerous, the power relations at the street-level of the mundane and taken-for-granted have been problematised as part of much larger social structures of power and discourse. 
Several Foucauldian tools were deployed in order to ensure that a focus on occupational therapy practices was maintained; three distinct research methods were utilised to access a range of heterogeneous genealogical information.  Firstly, an historical archival analysis of the four iterations of the Competencies for Registration for occupational therapists document (1990 to the current day) produced by the regulatory authority, the Occupational Therapy Board of New Zealand, was carried out.  Secondly, practice observations of occupational therapists working in different practice settings were analysed as three individual case studies. Concurrently with these two methods, a critical action method using a research blog was developed to create a medium for public discussion of practice through an open engagement with the profession. The combination of these three methods enabled access to a range of elements for analysis.  Many of these elements inter-linked, overlapped and connected to historically contingent networks of dominant power that have formed through the processes of colonisation, the establishment of the health system and normalised medical practices, and economic forms of governance. The nuances of how occupational therapy is practised at the street-level offered opportunities to contest the dominance of these networks. In all three case studies there was an unspoken understanding and a normalisation of materiality as an accepted and significant element of how the profession practised.  The material regimes of knowledge and material practices in these unspoken norms were highly productive and able to contest other lines of power.  Along with this alternate network of power, the most recent version of the Competencies for Registration offers a further opportunity for occupational therapists to contest dominant power relations in a way that could capitalise on the secure position the profession has developed through its material network of power.  Opportunities for alternate pathways of practice which privilege Te Ao Māori and Te Tiriti o Waitangi are a possibility in the legally sanctioned Competencies. The close connection of occupational therapy practices to real life material outcomes for other people, position the street-level doing of occupational therapists at a juncture where action and decision making can re-configure power relations. Re-thinking practice in terms of what the doing of occupational therapy does in relation to networks of power, is an opportunity for practitioners to enact policy at the street-level in ways that use their ability to influence power from the bottom up whilst being alert to the dangers presented by doing so.

text: Street-level bureaucracy and occupational therapy practices in Aotearoa New Zealand. A genealogical critique. As a human science that is also part of administering and supporting bureaucracy, occupational therapy functions in multi-layered networks of power  that support many different social structures. Occupational therapists’ work often involves operationalising health, education and social services at the street-level, positioning them between the aspirations of both policy and social activism and material life outcomes. Through a genealogical critique, this thesis problematises the practice of occupational therapy through a Foucauldian lens that views everything as dangerous. By viewing occupational therapy practice as dangerous, the power relations at the street-level of the mundane and taken-for-granted have been problematised as part of much larger social structures of power and discourse. 
Several Foucauldian tools were deployed in order to ensure that a focus on occupational therapy practices was maintained; three distinct research methods were utilised to access a range of heterogeneous genealogical information.  Firstly, an historical archival analysis of the four iterations of the Competencies for Registration for occupational therapists document (1990 to the current day) produced by the regulatory authority, the Occupational Therapy Board of New Zealand, was carried out.  Secondly, practice observations of occupational therapists working in different practice settings were analysed as three individual case studies. Concurrently with these two methods, a critical action method using a research blog was developed to create a medium for public discussion of practice through an open engagement with the profession. The combination of these three methods enabled access to a range of elements for analysis.  Many of these elements inter-linked, overlapped and connected to historically contingent networks of dominant power that have formed through the processes of colonisation, the establishment of the health system and normalised medical practices, and economic forms of governance. The nuances of how occupational therapy is practised at the street-level offered opportunities to contest the dominance of these networks. In all three case studies there was an unspoken understanding and a normalisation of materiality as an accepted and significant element of how the profession practised.  The material regimes of knowledge and material practices in these unspoken norms were highly productive and able to contest other lines of power.  Along with this alternate network of power, the most recent version of the Competencies for Registration offers a further opportunity for occupational therapists to contest dominant power relations in a way that could capitalise on the secure position the profession has developed through its material network of power.  Opportunities for alternate pathways of practice which privilege Te Ao Māori and Te Tiriti o Waitangi are a possibility in the legally sanctioned Competencies. The close connection of occupational therapy practices to real life material outcomes for other people, position the street-level doing of occupational therapists at a juncture where action and decision making can re-configure power relations. Re-thinking practice in terms of what the doing of occupational therapy does in relation to networks of power, is an opportunity for practitioners to enact policy at the street-level in ways that use their ability to influence power from the bottom up whilst being alert to the dangers presented by doing so.

year: 2018