title: Properties of mass-loading shocks: 1. Hydrodynamic considerations

authors: Zank, Gary P.

subjects: mass-loading shocks

abstract: The one-dimensional hydrodynamics of flows subjected to mass loading are considered anew, with particular emphasis placed on determining the properties of mass-loading shocks. This work has been motivated by recent observations of the outbound Halley bow shock (Neubauer et al., 1990), which cannot be understood in terms of simple hydrodynamical or magnetohydrodynamical descriptions. By including mass injection at the shock, we have investigated the properties of the Rankine-Hugoniot conditions on the basis of a geometric formulation of the entropy condition. Such a condition, which is more powerful than the usual thermodynamical formulation, serves to determine those solutions to the Rankine-Hugoniot conditions which correspond to a physically realizable downstream state. On this basis a concise theoretical description of hydrodynamic mass-loading shocks is obtained. We show that mass-loading shocks have more in common with combustion shocks than with ordinary nonreacting gas dynamical shocks. It is shown that for decelerated solutions to the Rankine-Hugoniot conditions to exist, the upstream flow speed u0 must satisfy u0 > ucrit > cs, where cs is the sound speed. Besides the usual supersonic-subsonic transition, mass-loading fronts can also admit a decelerating supersonic-supersonic transition, the structure of which consists of a sharp decrease in the flow velocity preceding a recovery and an increase in the final downstream flow speed. We suggest the possibility that such structures may describe the inbound Halley bow shock (Coates et al., 1987a). Both parallel and oblique shocks are considered, the primary difference being that oblique shocks are subjected to a shearing stress due to mass loading. It is conjectured that such a shearing may destabilize the shock.

text: Properties of mass-loading shocks: 1. Hydrodynamic considerations The one-dimensional hydrodynamics of flows subjected to mass loading are considered anew, with particular emphasis placed on determining the properties of mass-loading shocks. This work has been motivated by recent observations of the outbound Halley bow shock (Neubauer et al., 1990), which cannot be understood in terms of simple hydrodynamical or magnetohydrodynamical descriptions. By including mass injection at the shock, we have investigated the properties of the Rankine-Hugoniot conditions on the basis of a geometric formulation of the entropy condition. Such a condition, which is more powerful than the usual thermodynamical formulation, serves to determine those solutions to the Rankine-Hugoniot conditions which correspond to a physically realizable downstream state. On this basis a concise theoretical description of hydrodynamic mass-loading shocks is obtained. We show that mass-loading shocks have more in common with combustion shocks than with ordinary nonreacting gas dynamical shocks. It is shown that for decelerated solutions to the Rankine-Hugoniot conditions to exist, the upstream flow speed u0 must satisfy u0 > ucrit > cs, where cs is the sound speed. Besides the usual supersonic-subsonic transition, mass-loading fronts can also admit a decelerating supersonic-supersonic transition, the structure of which consists of a sharp decrease in the flow velocity preceding a recovery and an increase in the final downstream flow speed. We suggest the possibility that such structures may describe the inbound Halley bow shock (Coates et al., 1987a). Both parallel and oblique shocks are considered, the primary difference being that oblique shocks are subjected to a shearing stress due to mass loading. It is conjectured that such a shearing may destabilize the shock.

year: 1991

title: Optimising industrial hemp fibre for composites

authors: Pickering, Kim L.

abstract: The optimisation of New Zealand grown hemp fibre for inclusion in composites has been investigated. The optimum growing period was found to be 114 days, producing fibres with an average tensile strength of 857 MPa and a Young’s modulus of 58 GPa. An alkali treatment with 10wt% NaOH solution at a maximum processing temperature of 160o C with a hold time of 45 minutes was found to produce strong fibres with a low lignin content and good fibre separation. Although a good fit with the Weibull distribution function was obtained for single fibre strength, this did not allow for accurate scaling to strengths at different lengths. Alkali treated fibres, polypropylene and a maleated polypropylene (MAPP) coupling agent were compounded in a twin-screw extruder, and injection moulded into composite tensile test specimens. The strongest composite consisted of polypropylene with 40wt% fibre and 3wt% MAPP, and had a tensile strength of 47.2 MPa, and a Young’s modulus of 4.88 GPa.

text: Optimising industrial hemp fibre for composites The optimisation of New Zealand grown hemp fibre for inclusion in composites has been investigated. The optimum growing period was found to be 114 days, producing fibres with an average tensile strength of 857 MPa and a Young’s modulus of 58 GPa. An alkali treatment with 10wt% NaOH solution at a maximum processing temperature of 160o C with a hold time of 45 minutes was found to produce strong fibres with a low lignin content and good fibre separation. Although a good fit with the Weibull distribution function was obtained for single fibre strength, this did not allow for accurate scaling to strengths at different lengths. Alkali treated fibres, polypropylene and a maleated polypropylene (MAPP) coupling agent were compounded in a twin-screw extruder, and injection moulded into composite tensile test specimens. The strongest composite consisted of polypropylene with 40wt% fibre and 3wt% MAPP, and had a tensile strength of 47.2 MPa, and a Young’s modulus of 4.88 GPa.

year: 2007

title: Case roles / relations and discourse relations: A Maori language-based perspective

authors: Whaanga, Hēmi

subjects: case grammar

abstract: The overall aim of this research project is to explore case roles/ relations and discourse relations (referred to in this thesis as 'intra-propositional relations' and 'interpropositional relations' respectively) from the perspective of the Maori language. 
The thesis begins with an outline of the scope of the research and the approaches and methods used (Chapter 1). This is followed by a critical review of selected literature on case roles/ relations (intra-propositional relations) (see Chapter 2) and discourse relations (inter-propositional relations) (see Chapter 3) where it is noted that some of the relational theories and models appear to lack descriptive and/or explanatory adequacy. 
In Chapter 4, two models (an intra-propositional relational model and an interpropositional relational model) are developed on the basis of the critical review in Chapters 2 and 3, and these models are applied to a written corpus of Maori language texts, the primary aim being to track the ways in which intra-propositional and interpropositional relations are signalled in Maori. 
In Chapter 5, l supplement the corpus-based findings reported in Chapter 4 by reexamining the findings of two earlier studies from the perspective of the models introduced in Chapter 4. One of these earlier studies, reported in the early 1980s, is concerned with the distribution of prepositions in Maori in relation to case roles/ relations (intra-propositional relations); the other, produced much more recently (in 2001) is concerned with the signalling in Maori of a selection of what are referred to in that Work as 'semantico-pragmatic relations' (inter-propositional relations). 
Chapter 6 provides an overview of the research and a summary of the findings, together with an indication of its limitations, possible areas of application, and suggestions for future research.

text: Case roles / relations and discourse relations: A Maori language-based perspective The overall aim of this research project is to explore case roles/ relations and discourse relations (referred to in this thesis as 'intra-propositional relations' and 'interpropositional relations' respectively) from the perspective of the Maori language. 
The thesis begins with an outline of the scope of the research and the approaches and methods used (Chapter 1). This is followed by a critical review of selected literature on case roles/ relations (intra-propositional relations) (see Chapter 2) and discourse relations (inter-propositional relations) (see Chapter 3) where it is noted that some of the relational theories and models appear to lack descriptive and/or explanatory adequacy. 
In Chapter 4, two models (an intra-propositional relational model and an interpropositional relational model) are developed on the basis of the critical review in Chapters 2 and 3, and these models are applied to a written corpus of Maori language texts, the primary aim being to track the ways in which intra-propositional and interpropositional relations are signalled in Maori. 
In Chapter 5, l supplement the corpus-based findings reported in Chapter 4 by reexamining the findings of two earlier studies from the perspective of the models introduced in Chapter 4. One of these earlier studies, reported in the early 1980s, is concerned with the distribution of prepositions in Maori in relation to case roles/ relations (intra-propositional relations); the other, produced much more recently (in 2001) is concerned with the signalling in Maori of a selection of what are referred to in that Work as 'semantico-pragmatic relations' (inter-propositional relations). 
Chapter 6 provides an overview of the research and a summary of the findings, together with an indication of its limitations, possible areas of application, and suggestions for future research.

year: 2006