Observational properties of a kink unstable coronal loop

Aims. Previous work on the dynamics of the kink instability has concentrated on the evolution of the magnetic field and associated current sheets. Here we aim to determine the observational consequences of the kink instability in short coronal loops, particularly what images TRACE would record of such an instability. This paper concentrates on the internal m = 1 mode where the kink structure of the instability may not be apparent from the global field shape. This is most relevant to the observation of active region brightenings and coronal bright points. Methods. An existing fluid code was modified to include the TRACE temperature response function in order to calculate temporally and spatially averaged, line of sight images in the 171, 195 and 284 Å band passes for straight, kink unstable flux tubes. Results. Two new fluid effects of the kink instability are discovered: the circular enhancement of the density at the foot points and the appearance of a low density band running across the flux tube. The second of these effects is shown to be imagable by TRACE and hence would be a good candidate observational signature for an internal m = 1 kink unstable loop

Measures of Niche Overlap, II

An axiomatic basis for the construction of measures of niche overlap is analysed, and its implications are discussed, with particular reference to the more commonly used measures. A method of establishing that a measure of overlap complies with the axioms is put forward, making possible the construction of families of new measures. Certain extremal measures of overlap are also identifie

Digital preservation at Big Data scales: proposing a step-change in preservation system architectures

Purpose The purpose of this paper is to consider how digital preservation system architectures will support business analysis of large-scale collections of preserved resources, and the use of Big Data analyses by future researchers. Design/methodology/approach This paper reviews the architecture of existing systems, then discusses experimental surveys of large digital collections using existing digital preservation tools at Big Data scales. Finally, it introduces the design of a proposed new architecture to work with Big Data volumes of preserved digital resources – also based upon experience of managing a collection of 30 million digital images. Findings Modern visualisation tools enable business analyses based on file-related metadata, but most currently available systems need more of this functionality “out-of-the-box”. Scalability of preservation architecture to Big Data volumes depends upon the ability to run preservation processes in parallel, so indexes that enable effective sub-division of collections are vital. Not all processes scale easily: those that do not require complex management. Practical implications The complexities caused by scaling up to Big Data volumes can be seen as being at odds with preservation, where simplicity matters. However, the sustainability of preservation systems relates directly to their usefulness, and maintaining usefulness will increasingly depend upon being able to process digital resources at Big Data volumes. An effective balance between these conflicting situations must be struck. Originality/value Preservation systems are at a step-change as they move to Big Data scale architectures and respond to more technical research processes. This paper is a timely illustration of the state of play at this pivotal moment. The Polonsky Foundatio

Measures of Niche Overlap, I

Many methods of measuring niche overlap have been proposed, such as those of Renkonen, Morisita, and Horn. In this paper, conditions are put forward which overlap indices should reasonably be expected to satisfy. A general description of a good index is given, which covers as special cases those of the well-known indices which satisfy all the conditions. A mixture of the Renkonen and van Belle & Ahmad indices is suggested, as it has many desirable properties. The problem of estimating overlap from data is discussed briefl

Simulations of a lattice model of two-headed linear amphiphiles: influence of amphiphile asymmetry

Using a 2D lattice model, we conduct Monte Carlo simulations of micellar aggregation of linear-chain amphiphiles having two solvophilic head groups. In the context of this simple model, we quantify how the amphiphile architecture influences the critical micelle concentration (CMC), with a particular focus on the role of the asymmetry of the amphiphile structure. Accordingly, we study all possible arrangements of the head groups along amphiphile chains of fixed length $N=12$ and 16 molecular units. This set of idealized amphiphile architectures approximates many cases of symmetric and asymmetric gemini surfactants, double-headed surfactants and boloform surfactants. Consistent with earlier results, we find that the number of spacer units $s$ separating the heads has a significant influence on the CMC, with the CMC increasing with $s$ for $s<N/2$. In comparison, the influence of the asymmetry of the chain architecture on the CMC is much weaker, as is also found experimentally.Comment: 30 pages, 17 fgure

The triggering of MHD instabilities through photospheric footpoint motions

The results of 3D numerical simulations modelling the twisting of a coronal loop due to photospheric vortex motions are presented. The simulations are carried out using an initial purely axial field and an initial equilibrium configuration with twist, . The non-linear and resistive evolutions of the instability are followed. The magnetic field is twisted by the boundary motions into a loop which initially has boundary layers near the photospheric boundaries as has been suggested by previous work. The boundary motions increase the twist in the loop until it becomes unstable. For both cases the boundary twisting triggers the kink instability. In both cases a helical current structure wraps itself around the kinked central current. This current scales linearly with grid resolution indicating current sheet formation. For the cases studied 35-40% of the free magnetic energy is released. This is sufficient to explain the energy released in a compact loop flare

Simulations of a lattice model of two-headed linear amphiphiles: influence of amphiphile asymmetry

Using a 2D lattice model, we conduct Monte Carlo simulations of micellar aggregation of linear-chain amphiphiles having two solvophilic head groups. In the context of this simple model, we quantify how the amphiphile architecture influences the critical micelle concentration (CMC), with a particular focus on the role of the asymmetry of the amphiphile structure. Accordingly, we study all possible arrangements of the head groups along amphiphile chains of fixed length $N=12$ and 16 molecular units. This set of idealized amphiphile architectures approximates many cases of symmetric and asymmetric gemini surfactants, double-headed surfactants and boloform surfactants. Consistent with earlier results, we find that the number of spacer units $s$ separating the heads has a significant influence on the CMC, with the CMC increasing with $s$ for $s<N/2$. In comparison, the influence of the asymmetry of the chain architecture on the CMC is much weaker, as is also found experimentally.Comment: 30 pages, 17 fgure

The Organic Retail Market in Wales

This report on retail data provides an estimate of the value of the organic market in Wales and its borders, which shows the importance of this sector to the Welsh economy both directly and as a multiplier of the Welsh Government’s investment in organic farming under the Rural Development Plan (RDP) agri-environment schemes. The report combines data from three sources: Nielsen Scantrack which covers sales through ma-jor food and drink retailers (supermarkets) in Wales/West, surveys of Welsh organic businesses (independent retailers, processors, box schemes, farm shops and others) carried out by the Soil Association and data from the Welsh producer survey carried out by Organic Centre Wales. In addition, comments were invited from a number of industry experts

Processes and priorities in planning mathematics teaching

Insights into teachers' planning of mathematics reported here were gathered as part of a broader project examining aspects of the implementation of the Australian curriculum in mathematics (and English). In particular, the responses of primary and secondary teachers to a survey of various aspects of decisions that inform their use of curriculum documents and assessment processes to plan their teaching are discussed. Teachers appear to have a clear idea of the overall topic as the focus of their planning, but they are less clear when asked to articulate the important ideas in that topic. While there is considerable diversity in the processes that teachers use for planning and in the ways that assessment information informs that planning, a consistent theme was that teachers make active decisions at all stages in the planning process. Teachers use a variety of assessment data in various ways, but these are not typically data extracted from external assessments. This research has important implications for those responsible for supporting teachers in the transition to the Australian Curriculum: Mathematic