title: Linear theory of fast reconnection at an X-type neutral point

authors: Craig, Ian J.D.

abstract: A linear theory is developed for the dissipation of the free magnetic energy in small disturbances imposed on the potential field of an X-type neutral point. An eigenmode analysis, using cylindrical coordinates centered on the neutral point, extends the work of Craig & McClymont (1991) to include non-azimuthally symmetric perturbations on the flux function. We demonstrate that all physically significant disturbances, both reconnective and nonreconnective, decay resistively on a "fast" time scale ∼|ln η|, where η is the nondimensional resistivity. Thus resistive diffusion is remarkably effective as a dissipation mechanism for all classes of perturbation not only those modes which induce changes in the field topology. The fundamental reason for the fast dissipation is the focusing of wave energy onto the neutral point by the gradient in Alfvén speed. This occurs for all types of disturbances launched from the outer boundary, but reconnective modes propagate purely radially while nonreconnective modes correspond to waves with an azimuthal motion and a smaller wave speed in the radial direction. Dissipation of reconnective disturbances takes place in a diffusion region of diameter ≈η1/2 around the neutral point, on a time scale ∝ |ln η|2, but nonreconnective perturbations decay before penetrating to the neutral point, because of the increased path lengths due to their azimuthal motion. These modes release their energy in an annulus of radius ≈[(m3/ 4k)η]1/2, where m and k are azimuthal and radial wavenumbers: because of their longer transit time, nonreconnective waves decay on a |ln η|3 time scale. We conclude by discussing the significance of the linear theory within the general context of steady state and dynamic reconnection studies. It is pointed out that, dynamically, disturbances can be expected to focus explosively in the vicinity of the neutral point. This suggests the formation of a "flux pile-up" current layer in which the bulk of the magnetic energy is released as heat rather than kinetic energy of mass motion.

text: Linear theory of fast reconnection at an X-type neutral point A linear theory is developed for the dissipation of the free magnetic energy in small disturbances imposed on the potential field of an X-type neutral point. An eigenmode analysis, using cylindrical coordinates centered on the neutral point, extends the work of Craig & McClymont (1991) to include non-azimuthally symmetric perturbations on the flux function. We demonstrate that all physically significant disturbances, both reconnective and nonreconnective, decay resistively on a "fast" time scale ∼|ln η|, where η is the nondimensional resistivity. Thus resistive diffusion is remarkably effective as a dissipation mechanism for all classes of perturbation not only those modes which induce changes in the field topology. The fundamental reason for the fast dissipation is the focusing of wave energy onto the neutral point by the gradient in Alfvén speed. This occurs for all types of disturbances launched from the outer boundary, but reconnective modes propagate purely radially while nonreconnective modes correspond to waves with an azimuthal motion and a smaller wave speed in the radial direction. Dissipation of reconnective disturbances takes place in a diffusion region of diameter ≈η1/2 around the neutral point, on a time scale ∝ |ln η|2, but nonreconnective perturbations decay before penetrating to the neutral point, because of the increased path lengths due to their azimuthal motion. These modes release their energy in an annulus of radius ≈[(m3/ 4k)η]1/2, where m and k are azimuthal and radial wavenumbers: because of their longer transit time, nonreconnective waves decay on a |ln η|3 time scale. We conclude by discussing the significance of the linear theory within the general context of steady state and dynamic reconnection studies. It is pointed out that, dynamically, disturbances can be expected to focus explosively in the vicinity of the neutral point. This suggests the formation of a "flux pile-up" current layer in which the bulk of the magnetic energy is released as heat rather than kinetic energy of mass motion.

year: 1993

title: The Professionalization of Nursing: New Zealand as a Case Study

authors: Liu, Yue

subjects: Professionalization

abstract: Nursing has often been regarded by sociologists, the medical profession and even nurses themselves, as an occupational grouping which is semi - rather than fully - professionalised. This study is concerned with recognising the ‘professional project’ that has been undertaken by New Zealand nurses and assesses their progress towards professionalization by addressing two key research questions. Firstly, what are the historical and contemporary mechanisms by which nursing has attempted to secure professional status in New Zealand? Secondly, how do nursing organisations and nurses themselves seek to maintain and enhance their professional status? This study presents a review of historical and sociological literature with regard to nursing to portray its evolution from the colonial settlement of New Zealand until the present. Within the New Zealand context the professional project undertaken by nurses appears to have a proud history, and New Zealand nurses were the first in the world to achieve legislated registration. Despite this early recognition, progress towards achieving full professional status by this female dominated occupation has historically faced challenges from its male dominated counterpart in the form of the medical profession. The strength of nursing organisations and the establishment of formal nursing education have been two of the historical means by which professionalization for New Zealand nurses has been advanced. In order to examine contemporary perceptions about the processes through which nursing has been professionalized and how professional status is maintained, a series of eight semi-structured interviews were undertaken with a purposive sample of key informants from the state sector, nursing organisations and nursing educators. A qualitative analysis of the data collected showed that both nursing organisations and tertiary level qualifications had contributed to the achievement of professional status. The professional project had also been accelerated through working partnerships between nursing organisations and external stakeholders, as well as the establishment of standards that defined scopes of practice and codes of ethics. A diminishing public health budget and the increased presence of unregulated health workers were considered to be key threats to maintaining the professional status of nursing. This research concludes that despite the impression given by the international sociological literature that nursing is a semi-profession, nurses in New Zealand fulfil the claim to full professional status through their association with an exclusive body of knowledge, their ability to self-regulate and operate with a high degree of professional autonomy, as well as external recognition as a profession. However, professional status is dynamic, rather than fixed, and nurses will continue to strategically maintain and renegotiate their status in the face of future challenges.

text: The Professionalization of Nursing: New Zealand as a Case Study Nursing has often been regarded by sociologists, the medical profession and even nurses themselves, as an occupational grouping which is semi - rather than fully - professionalised. This study is concerned with recognising the ‘professional project’ that has been undertaken by New Zealand nurses and assesses their progress towards professionalization by addressing two key research questions. Firstly, what are the historical and contemporary mechanisms by which nursing has attempted to secure professional status in New Zealand? Secondly, how do nursing organisations and nurses themselves seek to maintain and enhance their professional status? This study presents a review of historical and sociological literature with regard to nursing to portray its evolution from the colonial settlement of New Zealand until the present. Within the New Zealand context the professional project undertaken by nurses appears to have a proud history, and New Zealand nurses were the first in the world to achieve legislated registration. Despite this early recognition, progress towards achieving full professional status by this female dominated occupation has historically faced challenges from its male dominated counterpart in the form of the medical profession. The strength of nursing organisations and the establishment of formal nursing education have been two of the historical means by which professionalization for New Zealand nurses has been advanced. In order to examine contemporary perceptions about the processes through which nursing has been professionalized and how professional status is maintained, a series of eight semi-structured interviews were undertaken with a purposive sample of key informants from the state sector, nursing organisations and nursing educators. A qualitative analysis of the data collected showed that both nursing organisations and tertiary level qualifications had contributed to the achievement of professional status. The professional project had also been accelerated through working partnerships between nursing organisations and external stakeholders, as well as the establishment of standards that defined scopes of practice and codes of ethics. A diminishing public health budget and the increased presence of unregulated health workers were considered to be key threats to maintaining the professional status of nursing. This research concludes that despite the impression given by the international sociological literature that nursing is a semi-profession, nurses in New Zealand fulfil the claim to full professional status through their association with an exclusive body of knowledge, their ability to self-regulate and operate with a high degree of professional autonomy, as well as external recognition as a profession. However, professional status is dynamic, rather than fixed, and nurses will continue to strategically maintain and renegotiate their status in the face of future challenges.

year: 2011

title: Tephras and New Zealand archaeology

authors: Lowe, David J.

subjects: tephrochronology

abstract: Establishing an accurate date for earliest Polynesian settlement in New Zealand is essential for understanding patterns of settlement and associated environmental impacts, and the processes and rates of cultural change in Eastern Polynesia. Tephra deposits from five volcanic centres, together with exotic sea-rafted pumice, provide isochronous constraints on the timing of earliest settlement and human impacts in northern New Zealand. A local basaltic tephra from Rangitoto Island (Auckland) and locally distributed andesitic tephras from Egmont volcano directly date human occupation to c. AD 1400–1450. Distal andesitic tephras (Tufa Trig Formation) from Mt Ruapehu, Tongariro volcanic centre, help constrain the timing of earliest anthropogenic deforestation signals in Hawke's Bay. Sea-rafted Loisels Pumice(s), although of uncertain stratigraphic reliability in places, overlies cultural remains that can be no younger than c. AD 1350 along the east coast, North Island. The regionally extensive rhyolitic Kaharoa Tephra, which erupted from Okataina volcano between c. AD  1300–1390, is the critical “settlement layer” datum for dating prehistory in the North Island: no human artefacts are recorded beneath it and the earliest inferred environmental impacts by humans are dated to c. AD  1280, just prior to its deposition. This maximum date matches the earliest radiocarbon dates derived for both settlement and human impacts from archaeological and natural sites (c. AD 1250), and implies that the onset of deforestation was essentially contemporaneous with initial settlement.
The widespread rhyolitic Taupo Tephra, which erupted from Taupo volcano c. AD 200, provides an isochronous benchmark well before earliest settlement. The tephra may coincide approximately with a putative earlier transient contact in New Zealand based on Pacific rat-bone (Rattus exulans) dates. More precise calendrical dates on the tephras—via dendrochronology or ice-core records or other dating methods—would help refine assessment of the timing of earliest settlement, while extending the distributional range of critical tephra layers, through application of crypto-tephra analysis, could lead to a greater understanding of settlement patterns.

text: Tephras and New Zealand archaeology Establishing an accurate date for earliest Polynesian settlement in New Zealand is essential for understanding patterns of settlement and associated environmental impacts, and the processes and rates of cultural change in Eastern Polynesia. Tephra deposits from five volcanic centres, together with exotic sea-rafted pumice, provide isochronous constraints on the timing of earliest settlement and human impacts in northern New Zealand. A local basaltic tephra from Rangitoto Island (Auckland) and locally distributed andesitic tephras from Egmont volcano directly date human occupation to c. AD 1400–1450. Distal andesitic tephras (Tufa Trig Formation) from Mt Ruapehu, Tongariro volcanic centre, help constrain the timing of earliest anthropogenic deforestation signals in Hawke's Bay. Sea-rafted Loisels Pumice(s), although of uncertain stratigraphic reliability in places, overlies cultural remains that can be no younger than c. AD 1350 along the east coast, North Island. The regionally extensive rhyolitic Kaharoa Tephra, which erupted from Okataina volcano between c. AD  1300–1390, is the critical “settlement layer” datum for dating prehistory in the North Island: no human artefacts are recorded beneath it and the earliest inferred environmental impacts by humans are dated to c. AD  1280, just prior to its deposition. This maximum date matches the earliest radiocarbon dates derived for both settlement and human impacts from archaeological and natural sites (c. AD 1250), and implies that the onset of deforestation was essentially contemporaneous with initial settlement.
The widespread rhyolitic Taupo Tephra, which erupted from Taupo volcano c. AD 200, provides an isochronous benchmark well before earliest settlement. The tephra may coincide approximately with a putative earlier transient contact in New Zealand based on Pacific rat-bone (Rattus exulans) dates. More precise calendrical dates on the tephras—via dendrochronology or ice-core records or other dating methods—would help refine assessment of the timing of earliest settlement, while extending the distributional range of critical tephra layers, through application of crypto-tephra analysis, could lead to a greater understanding of settlement patterns.

year: 2000