title: Current singularities in line-tied three-dimensional magnetic fields

authors: Craig, Ian J.D.

subjects: Science & Technology

abstract: This paper considers the current distributions that derive from finite amplitude perturbations of line-tied magnetic fields comprising hyperbolic field structures. The initial equilibrium on which we principally focus is a planar magnetic X-point threaded by a uniform axial field. This field is line-tied on all surfaces but subject to threedimensional (3D) disturbances that alter the initial topology. Results of ideal relaxation simulations are presented which illustrate how intense current structures form that can be related, through the influence of line-tying, to the quasi-separatrix layers (QSLs) of the initial configuration. It is demonstrated that the location within the QSL that attracts the current, and its scaling properties, are strongly dependent on the relative dimensions of the QSL with respect to the line-tied boundaries. These results are contrasted with the behavior of a line-tied 3D field containing an isolated null point. In this case, it is found that the dominant current always forms at the null, but that the collapse is inhibited when the null is closer to a line-tied boundary.

text: Current singularities in line-tied three-dimensional magnetic fields This paper considers the current distributions that derive from finite amplitude perturbations of line-tied magnetic fields comprising hyperbolic field structures. The initial equilibrium on which we principally focus is a planar magnetic X-point threaded by a uniform axial field. This field is line-tied on all surfaces but subject to threedimensional (3D) disturbances that alter the initial topology. Results of ideal relaxation simulations are presented which illustrate how intense current structures form that can be related, through the influence of line-tying, to the quasi-separatrix layers (QSLs) of the initial configuration. It is demonstrated that the location within the QSL that attracts the current, and its scaling properties, are strongly dependent on the relative dimensions of the QSL with respect to the line-tied boundaries. These results are contrasted with the behavior of a line-tied 3D field containing an isolated null point. In this case, it is found that the dominant current always forms at the null, but that the collapse is inhibited when the null is closer to a line-tied boundary.

year: 2014-06-20

title: Characterizing an image intensifier in an full-field range image system

authors: Payne, Andrew D.

subjects: image intensifier

abstract: We are developing a high precision full-field range imaging system. An integral component in this system is an image intensifier, which is modulated at frequencies up to 100 MHz. The range measurement precision is dictated by the image intensifier performance, in particular, the achievable modulation frequency, modulation depth, and waveform shape. By characterizing the image intensifier response, undesirable effects can be observed and quantified with regards to the consequence on the resulting range measurements, and the optimal operating conditions can be selected to minimize these disturbances. The characterization process utilizes a pulsed laser source to temporally probe the gain of the image intensifier. The laser is pulsed at a repetition rate slightly different to the image intensifier modulation frequency, producing a continuous phase shift between the two signals. A charge coupled device samples the image intensifier output, capturing the response over a complete modulation period. Deficiencies in our measured response are clearly identifiable and simple modifications to the configuration of our electrical driver circuit improve the modulation performance.

text: Characterizing an image intensifier in an full-field range image system We are developing a high precision full-field range imaging system. An integral component in this system is an image intensifier, which is modulated at frequencies up to 100 MHz. The range measurement precision is dictated by the image intensifier performance, in particular, the achievable modulation frequency, modulation depth, and waveform shape. By characterizing the image intensifier response, undesirable effects can be observed and quantified with regards to the consequence on the resulting range measurements, and the optimal operating conditions can be selected to minimize these disturbances. The characterization process utilizes a pulsed laser source to temporally probe the gain of the image intensifier. The laser is pulsed at a repetition rate slightly different to the image intensifier modulation frequency, producing a continuous phase shift between the two signals. A charge coupled device samples the image intensifier output, capturing the response over a complete modulation period. Deficiencies in our measured response are clearly identifiable and simple modifications to the configuration of our electrical driver circuit improve the modulation performance.

year: 2008

title: Aihe Pepene

authors: Hart, Philip

abstract: Sharing the same illustrious whakapapa as his brother Reha Aperahama, Aihe Pepene was prominent when living in the Thames district before settling at Te Aroha in 1878. When speculators tried to acquire the Thames foreshore from Pepene and others in 1870, he became involved in the subsequent legal actions over unpaid promissory notes. Later he would acquire interests in many blocks of land, and received a steady income by leasing or selling these plus his share in the goldfields revenue. When the Aroha Block was considered by the land court for the last time, in 1878, he conducted the case for Ngati Rahiri.
He invested in four Hauraki goldfields, and was briefly an owner and skipper of two small river steamers, an unsuccessful endeavour that resulted in his being forced to sell more land to meet his debts. Once his 1880 and 1881 financial difficulties were resolved, no more such problems recurred. 
A leading rangatira in Hauraki generally as well as at Te Aroha, he would be elected to a Maori Committee that was soon revealed to have no significance. Closely involved with Pakeha, he assisted settlement, and his loyalty to the Crown was illustrated by his becoming an officer in the Thames Native Volunteer Corps. A member of the Church of England for many years, like many Maori he became a Mormon, a faith perhaps more appropriate to his private life, for he had more than one wife, notoriously eloping with the wife of a more senior rangatira despite already being married.

text: Aihe Pepene Sharing the same illustrious whakapapa as his brother Reha Aperahama, Aihe Pepene was prominent when living in the Thames district before settling at Te Aroha in 1878. When speculators tried to acquire the Thames foreshore from Pepene and others in 1870, he became involved in the subsequent legal actions over unpaid promissory notes. Later he would acquire interests in many blocks of land, and received a steady income by leasing or selling these plus his share in the goldfields revenue. When the Aroha Block was considered by the land court for the last time, in 1878, he conducted the case for Ngati Rahiri.
He invested in four Hauraki goldfields, and was briefly an owner and skipper of two small river steamers, an unsuccessful endeavour that resulted in his being forced to sell more land to meet his debts. Once his 1880 and 1881 financial difficulties were resolved, no more such problems recurred. 
A leading rangatira in Hauraki generally as well as at Te Aroha, he would be elected to a Maori Committee that was soon revealed to have no significance. Closely involved with Pakeha, he assisted settlement, and his loyalty to the Crown was illustrated by his becoming an officer in the Thames Native Volunteer Corps. A member of the Church of England for many years, like many Maori he became a Mormon, a faith perhaps more appropriate to his private life, for he had more than one wife, notoriously eloping with the wife of a more senior rangatira despite already being married.

year: 2016