title: Coronal heating distribution due to low-frequency, wave-driven turbulence

authors: Dmitruk, Pablo

subjects: MHD

abstract: The heating of the lower solar corona is examined using numerical simulations and theoretical models of magnetohydrodynamic turbulence in open magnetic regions. A turbulent energy cascade to small length scales perpendicular to the mean magnetic field can be sustained by driving with low-frequency Alfvén waves reflected from mean density and magnetic field gradients. This mechanism deposits energy efficiently in the lower corona, and we show that the spatial distribution of the heating is determined by the mean density through the Alfvén speed profile. This provides a robust heating mechanism which can explain observed high coronal temperatures and accounts for the significant heating (per unit volume) distribution below 2 solar radii needed in models of the origin of the solar wind. The obtained heating per unit mass, on the other hand, is much more extended, indicating that the heating on a per-particle basis persists throughout all the lower coronal region considered here.

text: Coronal heating distribution due to low-frequency, wave-driven turbulence The heating of the lower solar corona is examined using numerical simulations and theoretical models of magnetohydrodynamic turbulence in open magnetic regions. A turbulent energy cascade to small length scales perpendicular to the mean magnetic field can be sustained by driving with low-frequency Alfvén waves reflected from mean density and magnetic field gradients. This mechanism deposits energy efficiently in the lower corona, and we show that the spatial distribution of the heating is determined by the mean density through the Alfvén speed profile. This provides a robust heating mechanism which can explain observed high coronal temperatures and accounts for the significant heating (per unit volume) distribution below 2 solar radii needed in models of the origin of the solar wind. The obtained heating per unit mass, on the other hand, is much more extended, indicating that the heating on a per-particle basis persists throughout all the lower coronal region considered here.

year: 2002

title: Propagating action potentials and the regeneration of acetabularia mediterranea: a pilot study

authors: Lertsithichai, Somak

abstract: A study of the relationship between the cell membrane electrical activity and the observed polar regeneration in anucleate isolated stalk segments of Acetabularia may help answer the question of how a single cell can ‘break symmetry’ and establish a definite polarity. Such studies have been carried out extensively by Novak and Bentrup and their colleagues since 1972, but their results contain unresolved inconsistencies and although their experimental technique overcomes the problems arising from conventional microelectrode techniques, it gives a restricted and electrically perturbative environment for the cell.
In an attempt to overcome these limitations the work in this thesis describes the development of a new technique for measuring the electrical activity of the cell membrane with minimum perturbation from the measuring system. In addition it gives more precise and detailed information about the region of action potential initiation and subsequent propagation. 
The results of measurements using this technique on a variety of intact cells and various cell segments, including anucleate stalk segments are presented and discussed. The results provide strong evidence for the hypothesis that the region of action potential initiation is strongly correlated with the region of current growth. They do not however appear to provide any support for the suggestion of Novak and Bentrup that propagating action potentials are an essential component of the mechanism for ‘symmetry breaking’ in initially unpolarised anucleate stalk segments.

text: Propagating action potentials and the regeneration of acetabularia mediterranea: a pilot study A study of the relationship between the cell membrane electrical activity and the observed polar regeneration in anucleate isolated stalk segments of Acetabularia may help answer the question of how a single cell can ‘break symmetry’ and establish a definite polarity. Such studies have been carried out extensively by Novak and Bentrup and their colleagues since 1972, but their results contain unresolved inconsistencies and although their experimental technique overcomes the problems arising from conventional microelectrode techniques, it gives a restricted and electrically perturbative environment for the cell.
In an attempt to overcome these limitations the work in this thesis describes the development of a new technique for measuring the electrical activity of the cell membrane with minimum perturbation from the measuring system. In addition it gives more precise and detailed information about the region of action potential initiation and subsequent propagation. 
The results of measurements using this technique on a variety of intact cells and various cell segments, including anucleate stalk segments are presented and discussed. The results provide strong evidence for the hypothesis that the region of action potential initiation is strongly correlated with the region of current growth. They do not however appear to provide any support for the suggestion of Novak and Bentrup that propagating action potentials are an essential component of the mechanism for ‘symmetry breaking’ in initially unpolarised anucleate stalk segments.

year: 1980

title: Putting Sylvia in her place: history, geographical theory and the “New” Education

authors: Middleton, Sue

subjects: Sylvia Ashton-Warner

abstract: New Zealander Sylvia Ashton-Warner, a teacher in remote rural Mori schools in the 1940s-1950s, became internationally renowned as a novelist and educational theorist. Earlier commentators portrayed her educational theory as in conflict with those of her time and place, but recent studies conceptualise them as enabled by it. While space/place has often been considered the preserve of the geographer and time that of the historian, Henri Lefebvre and others suggest that: “these issues need to be thought together rather than separately” and that macro-, meso- and micro-levels of analysis be engaged simultaneously. The author traces how conceptual, linguistic, sensory and intellectual resources of the global “New Education” movement extended into the tiny bush-encircled Mori communities in which Sylvia taught and wrote in the 1940s-1950s and surfaced in her writing. The article zooms in and out between the “the immensity of the global” (the New Education, the Second World War) and “the intimately tiny” (her classroom and home). The “data” include Sylvia's non-fiction education texts and official documents of her time: school curricula, education policy documents, Ministerial and Inspectors' reports. What Lefebvre terms a “Rhythm analysis” of Ashton-Warner's educational writing shows intermingled pulses of domestic life, routines of educational bureaucracy, cycles of nature, and cataclysms of world events. It is important for historians to study “the where rather than just the when with location and landscape central parts of the analysis”.

text: Putting Sylvia in her place: history, geographical theory and the “New” Education New Zealander Sylvia Ashton-Warner, a teacher in remote rural Mori schools in the 1940s-1950s, became internationally renowned as a novelist and educational theorist. Earlier commentators portrayed her educational theory as in conflict with those of her time and place, but recent studies conceptualise them as enabled by it. While space/place has often been considered the preserve of the geographer and time that of the historian, Henri Lefebvre and others suggest that: “these issues need to be thought together rather than separately” and that macro-, meso- and micro-levels of analysis be engaged simultaneously. The author traces how conceptual, linguistic, sensory and intellectual resources of the global “New Education” movement extended into the tiny bush-encircled Mori communities in which Sylvia taught and wrote in the 1940s-1950s and surfaced in her writing. The article zooms in and out between the “the immensity of the global” (the New Education, the Second World War) and “the intimately tiny” (her classroom and home). The “data” include Sylvia's non-fiction education texts and official documents of her time: school curricula, education policy documents, Ministerial and Inspectors' reports. What Lefebvre terms a “Rhythm analysis” of Ashton-Warner's educational writing shows intermingled pulses of domestic life, routines of educational bureaucracy, cycles of nature, and cataclysms of world events. It is important for historians to study “the where rather than just the when with location and landscape central parts of the analysis”.

year: 2011