Catastrophe versus instability for the eruption of a toroidal solar magnetic flux rope

The onset of a solar eruption is formulated here as either a magnetic catastrophe or as an instability. Both start with the same equation of force balance governing the underlying equilibria. Using a toroidal flux rope in an external bipolar or quadrupolar field as a model for the current-carrying flux, we demonstrate the occurrence of a fold catastrophe by loss of equilibrium for several representative evolutionary sequences in the stable domain of parameter space. We verify that this catastrophe and the torus instability occur at the same point; they are thus equivalent descriptions for the onset condition of solar eruptions.Comment: V2: update to conform to the published article; new choice for internal inductance of torus; updated Fig. 2; new Figs. 3, 5, and

Indeterminacy and instability in Petschek reconnection

We explain two puzzling aspects of Petschek's model for fast reconnection. One is its failure to occur in plasma simulations with uniform resistivity. The other is its inability to provide anything more than an upper limit for the reconnection rate. We have found that previously published analytical solutions based on Petschek's model are structurally unstable if the electrical resistivity is uniform. The structural instability is associated with the presence of an essential singularity at the X-line that is unphysical. By requiring that such a singularity does not exist, we obtain a formula that predicts a specific rate of reconnection. For uniform resistivity, reconnection can only occur at the slow, Sweet-Parker rate. For nonuniform resistivity, reconnection can occur at a much faster rate provided that the resistivity profile is not too flat near the X-line. If this condition is satisfied, then the scale length of the nonuniformity determines the reconnection rate

Microbial metagenome-assembled genomes of the Fram Strait from short and long read sequencing platforms

The impacts of climate change on the Arctic Ocean are manifesting throughout the ecosystem at an unprecedented rate. Of global importance are the impacts on heat and freshwater exchange between the Arctic and North Atlantic Oceans. An expanding Atlantic influence in the Arctic has accelerated sea-ice decline, weakened water column stability and supported the northward shift of temperate species. The only deep-water gateway connecting the Arctic and North Atlantic and thus, fundamental for these exchange processes is the Fram Strait. Previous research in this region is extensive, however, data on the ecology of microbial communities is limited, reflecting the wider bias towards temperate and tropical latitudes. Therefore, we present 14 metagenomes, 11 short-read from Illumina and three long-read from PacBio Sequel II, of the 0.2–3 µm fraction to help alleviate such biases and support future analyses on changing ecological patterns. Additionally, we provide 136 species-representative, manually refined metagenome-assembled genomes which can be used for comparative genomics analyses and addressing questions regarding functionality or distribution of taxa

Diversity and biomass dynamics of unicellular marine fungi during a spring phytoplankton bloom

Microbial communities have important functions during spring phytoplankton blooms, regulating bloom dynamics and processing organic matter. Despite extensive research into such processes, an in-depth assessment of the fungal component is missing, especially for the smaller size fractions. We investigated the dynamics of unicellular mycoplankton during a spring phytoplankton bloom in the North Sea by 18S rRNA gene tag sequencing and a modified CARD-FISH protocol. Visualization and enumeration of dominant taxa revealed unique cell count patterns that varied considerably over short time scales. The Rozellomycota sensu lato (s.l.) reached a maximum of 10(5) cells L-1, being comparable to freshwater counts. The abundance of Dikarya surpassed previous values by two orders of magnitude (10(5) cells L-1) and the corresponding biomass (maximum of 8.9 mg C m(-3)) was comparable to one reported for filamentous fungi with assigned ecological importance. Our results show that unicellular fungi are an abundant and, based on high cellular ribosome content and fast dynamics, active part of coastal microbial communities. The known ecology of the visualized taxa and the observed dynamics suggest the existence of different ecological niches that link primary and secondary food chains, highlighting the importance of unicellular fungi in food web structures and carbon transfer

Plasma Relaxation and Topological Aspects in Hall Magnetohydrodynamics

Parker's formulation of isotopological plasma relaxation process in magnetohydrodynamics (MHD) is extended to Hall MHD. The torsion coefficient alpha in the Hall MHD Beltrami condition turns out now to be proportional to the "potential vorticity." The Hall MHD Beltrami condition becomes equivalent to the "potential vorticity" conservation equation in two-dimensional (2D) hydrodynamics if the Hall MHD Lagrange multiplier beta is taken to be proportional to the "potential vorticity" as well. The winding pattern of the magnetic field lines in Hall MHD then appears to evolve in the same way as "potential vorticity" lines in 2D hydrodynamics

Ethnicity and children

This article explores field research that sought to find out how young children explored difference and identity in a multi-ethnic early years setting and whether this influenced their peer interactions

Realising a vision - a partnership approach to education capturing the enterprising spirit of the young people of North Tyneside

This paper describes and explains how three separate initiatives, for linking education with business and industry, were integrated to give a model for action in widely different types of school. Each author worked on one initiative, and this model was then the outcome of combining their expertise and experience. The rationale and philosophy behind the following three initiatives was explored. Provision of training days for advisory staff on the potential use of the Banking Information Service multi-media resource "Financial Planning and Management of Design Technology Projects". An interdisciplinary enquiry by the Advisory Team for Technology of North Tyneside Education Authority into the delivery of the National Curriculum within the context of a local initiative entitled "Schools Mean Business". Commissions undertaken by student teachers in connection with the TVEI/Initial Teacher Training Programme of Newcastle Polytechnic. The outcome was the provision of a model for action, to be described fully in the paper, within five local authority schools; a first school, a middle school, two special schools and a comprehensive school. Each school established its own partnerships between one another, with higher education via student commissions, with local industry, with initiatives led by local councils, and in a number of other ways. Schools set up programmes of study using the process of technology, exploring the implementation of the National Curriculum beyond subject boundaries - programmes requiring trust, flexibility, and a vision of education as a whole. The work done in the schools will also be illustrated in our poster presentations at the conference

Age-related differences in dual task walking: a cross sectional study

<p>Abstract</p> <p>Background</p> <p>Variability in stride velocity during walking characterizes gait instability and predicts falling in older individuals. Walking while executing a cognitive task is also associated with increased risk of falling, particularly in older adults. Variability in stride velocity, particularly during dual task walking conditions, may differ between younger and older individuals. The purpose of this study was to examine whether gait velocity and variability in stride velocity differ between older community-dwelling women and younger women during dual task walking.</p> <p>Methods</p> <p>Twenty-three older (80 ± 9 years) and 19 younger (23 ± 2 years) women walked under each of two conditions: (1) walking at a self-selected velocity and (2) walking at a self-selected velocity while incrementally counting backwards. Gait velocity and variability in stride velocity were measured with GAITRite^®instrumentation.</p> <p>Results</p> <p>Gait velocity decreased and variability in stride variability increased, in both groups, during dual task walking. The relative reduction in gait velocity and the magnitude of variability in stride velocity were greater in the older subjects than younger subjects.</p> <p>Conclusion</p> <p>The gait changes observed in dual task walking characterize reduced gait stability and indicate that cognitively demanding tasks during walking have a destabilizing effect on gait that may place older persons at greater risk of falls.</p

A multiwavelength radial velocity search for planets around the brown dwarf LP 944-20

The nearby brown dwarf LP 944-20 has been monitored for radial velocity variability at optical and near-infrared wavelengths using the VLT/UVES and the Keck/NIRSPEC spectrographs, respectively. The UVES radial velocity data obtained over 14 nights spanning a baseline of 841 days shows significant variability with an amplitude of 3.5 km s$^{-1}$. The periodogram analysis of the UVES data indicates a possible period between 2.5 hours and 3.7 hours, which is likely due to the rotation of the brown dwarf. However, the NIRSPEC data obtained over 6 nights shows an rms dispersion of only 0.36 km s$^{-1}$ and do not follow the periodic trend. These results indicate that the variability seen with UVES is likely to be due to rotationally modulated inhomogeneous surface features. We suggest that future planet searches around very low-mass stars and brown dwarfs using radial velocities will be better conducted in the near-infrared than in the optical.Comment: accepted by ApJ Letter

Locating current sheets in the solar corona

Current sheets are essential for energy dissipation in the solar corona, in particular by enabling magnetic reconnection. Unfortunately, sufficiently thin current sheets cannot be resolved observationally and the theory of their formation is an unresolved issue as well. We consider two predictors of coronal current concentrations, both based on geometrical or even topological properties of a force free coronal magnetic field. First, there are separatrices related to magnetic nulls. Through separatrices the magnetic connectivity changes discontinuously. Coronal magnetic nulls are, however, very rare. At second, inspired by the concept of generalized magnetic reconnection without nulls, quasi-separatrix layers (QSL) were suggested. Through QSL the magnetic connectivity changes continuously, though strongly. The strength of the connectivity change can be quantified by measuring the squashing of the flux tubes which connect the magnetically conjugated photospheres. We verify the QSL and separatrix concepts by comparing the sites of magnetic nulls and enhanced squashing with the location of current concentrations in the corona. Due to the known difficulties of their direct observation we simulated the coronal current sheets by numerically calculating the response of the corona to energy input from the photosphere heating a simultaneously observed EUV Bright Point. We did not find coronal current sheets not at the separatrices but at several QSL locations. The reason is that although the geometrical properties of force free extrapolated magnetic fields can indeed, hint at possible current concentrations, a necessary condition for current sheet formation is the local energy input into the corona