Marginal states of the resistive tearing mode with flow in cylindrical geometry

The linear stability of tearing modes in a cylindrical plasma subject to a sub-Alfvénic equilibrium shear flow along the equilibrium magnetic field is considered. The equations in the resistive boundary layer at the rational surface are solved numerically using a Fourier transform combined with a finite-element approach. The behaviour of the growth rate as a function of the flow and the various parameters (including a perpendicular fluid viscosity) is obtained. Marginal stability curves showing the dependence of the familiar matching parameter Δ' with flow and shear are also given

Interior layers in a reaction-diffusion equation with a discontinuous diffusion coefficient

In this paper a problem arising in the modelling of semiconductor devices motivates the study of singularly perturbed differential equations of reaction–diffusion type with discontinuous data. The solutions of such problems typically contain interior layers where the gradient of the solution changes rapidly. Parameter–uniform methods based on piecewise–uniform Shishkin meshes are constructed and analysed for such problems. Numerical results are presented to support the theoretical results and to illustrate the benefits of using a piecewise–uniform Shishkin mesh over the use of uniform meshes in the simulation of a simple semiconductor device

A singularly perturbed convection–diffusion problem with a moving pulse

A singularly perturbed parabolic equation of convection–diffusion type is examined. Initially the solution approximates a concentrated source. This causes an interior layer to form within the domain for all future times. Using a suitable transformation, a layer adapted mesh is constructed to track the movement of the centre of the interior layer. A parameter-uniform numerical method is then defined, by combining the backward Euler method and a simple upwinded finite difference operator with this layer-adapted mesh. Numerical results are presented to illustrate the theoretical error bounds established

Singularly perturbed initial-boundary value problem with a pulse in the initial condition

A singularly perturbed parabolic equation of reaction-diffusion type is examined. Initially the solution approximates a concentrated source, which causes an interior layer to form within the solution for all future times. Combining a classical finite difference operator with a layer-adapted mesh, parameter-uniform convergence is established. Numerical results are presented to illustrate the theoretical error bounds

MoviCompile : An LLVM based compiler for heterogeneous SIMD code generation

Numerous applications in communication and multimedia domains show significant data-level parallelism (DLP). The amount of DLP varies between applications in the same domain or even within a single application. Most architectures support a single vector-, SIMD-width which may not be optimal. This may cause performance and energy inefficiency. We propose the use of multiple (heterogeneous) vector-widths to better serve applications with varying DLP. The SHAVE (Streaming Hybrid Architecture Vector Engine) VLIW vector processor shown in Figure 1 is an example of such an architecture. SHAVE is a unique VLIW processor that provides hardware support for native 32-bit (short) and 128-bit (long) vector operations. Vector arithmetic unit (VAU) supports 128-bit vector arithmetic of 8/16/32-bit integer and 16/32-bit floating point types. Scalar arithmetic unit (SAU) supports 32-bit vector arithmetic of 8/16-bit integer and 16-bit floating point types. The moviCompile compiler is an LLVM based commercial compiler targeting code generation for SHAVE processor family. The moviCompile compiler is capable of SIMD code generation for 128-bit (long) and 64-bit vector operations. This work focuses on compiler backend support for 32-bit (short) vector operations. More specifically, this work aims to generate SIMD code for short vector types (e.g. 4 x i8, 2 x i16, 2 x f16) that can be executed on 32-bit SAU next to the 128/64-bit SIMD code. As a result, moviCompile is able to generate heterogeneous assembly code consisting of both short and long vector SIMD operations. Currently, we are testing the compiler using TSVC (Test Suite for Vectorizing Compilers) and intend to measure the performance improvements

How should we measure online learning activity?

The proliferation of Web-based learning objects makes finding and evaluating resources a considerable hurdle for learners to overcome. While established learning analytics methods provide feedback that can aid learner evaluation of learning resources, the adequacy and reliability of these methods is questioned. Because engagement with online learning is different from other Web activity, it is important to establish pedagogically relevant measures that can aid the development of distinct, automated analysis systems. Content analysis is often used to examine online discussion in educational settings, but these instruments are rarely compared with each other which leads to uncertainty regarding their validity and reliability. In this study, participation in Massive Open Online Course (MOOC) comment forums was evaluated using four different analytical approaches: the Digital Artefacts for Learning Engagement (DiAL-e) framework, Bloom's Taxonomy, Structure of Observed Learning Outcomes (SOLO) and Community of Inquiry (CoI). Results from this study indicate that different approaches to measuring cognitive activity are closely correlated and are distinct from typical interaction measures. This suggests that computational approaches to pedagogical analysis may provide useful insights into learning processes

Biodigital publics: personal genomes as digital media artifacts

The recent proliferation of personal genomics and direct-to-consumer (DTC) genomics has attracted much attention and publicity. Concern around these developments has mainly focused on issues of biomedical regulation and hinged on questions of how people understand genomic information as biomedical and what meaning they make of it. However, this publicity amplifies genome sequences which are also made as internet texts and, as such, they generate new reading publics. The practices around the generation, circulation and reading of genome scans do not just raise questions about biomedical regulation, they also provide the focus for an exploration of how contemporary public participation in genomics works. These issues around the public features of DTC genomic testing can be pursued through a close examination of the modes of one of the best known providers—23andMe. In fact, genome sequences circulate as digital artefacts and, hence, people are addressed by them. They are read as texts, annotated and written about in browsers, blogs and wikis. This activity also yields content for media coverage which addresses an indefinite public in line with Michael Warner’s conceptualisation of publics. Digital genomic texts promise empowerment, personalisation and community, but this promise may obscure the compliance and proscription associated with these forms. The kinds of interaction here can be compared to those analysed by Andrew Barry. Direct-to-consumer genetics companies are part of a network providing an infrastructure for genomic reading publics and this network can be mapped and examined to demonstrate the ways in which this formation both exacerbates inequalities and offers possibilities for participation in biodigital culture

The reproductive biology of the exploited razor clam, Ensis siliqua, in the Irish Sea

Knowledge of the reproductive cycle of a species is a prerequisite for sustainable management of a fishery. The infaunal marine bivalve, Ensis siliqua, is a commercially important species in Europe, and is exploited in many countries, including Ireland, where it is sold by wet weight. Seasonal variations in the reproductive cycle of subtidal razor clams from the Skerries region of the Irish Sea, an important fisheries area, were examined between June 2010 and September 2011 while monitoring weight. Histological examination revealed that the E. siliqua sex-ratio was not different from parity, and no hermaphrodites were observed in the samples collected. In the summer months of 2010 all female clams were either spent or in early development, with just a small percentage of males still spawning. The gonads of both sexes developed over the autumn and winter months of 2010, with the first spawning individuals recorded in January 2011. Spawning peaked in March 2011, but unlike in 2010, spawning continued through June and July with all animals spent in August 2011. The earlier and longer spawning period found in this species in 2011 compared to 2010 may have been due to the colder than normal temperature observed during the winter of 2010 plus the relatively warmer temperatures of Spring 2011, which could have affected the gametogenic development of E. siliqua in the Irish Sea. It was noted that wet weight dropped in the summer months of both years, immediately after the spawning period which may impact on the practicality of fishing for this species during this period. Timing of development and spawning is compared with other sites in the Irish Sea and elsewhere in Europe, including the Iberian Peninsula

Restricted diet in a vulnerable native turtle, Malaclemys terrapin (Schoepff), on the oceanic islands of Bermuda

Diamondback Terrapins (Malaclemys terrapin) are native to Bermuda, presently inhabiting only four small brackish-water ponds. Their foraging ecology was investigated using direct observation, fecal analysis, and necropsy. They do not have as varied a diet as reported from their North American range. Small gastropods (<3 mm shell height) were found in 66.7% of fecal samples and made up 97.3% of animal material dry mass, thus dominating their diet. Scavenged fish and other vertebrates (19% of samples overall), plus terrestrial arthropods (14.3% of samples) were other common items. Polychaete worms and bivalves each occurred in less than 3% of fecal samples. Pond sediment was found in 74% of the samples, probably incidentally ingested while foraging (by oral dredging) for the gastropods. The distribution and abundance of arthropods and molluscs within the terrapins’ brackish-water environment were assessed in three different habitats; pond benthos, mangrove swamp, and grass-dominated marsh. These indicated that Bermuda’s terrapins do not fully exploit the food resources present. On Bermuda M. terrapin is basically a specialist microphagous molluscivore and mainly forages by deposit-feeding on gastropods living in soft sediments. This dietary restriction has made them particularly vulnerable to environmental contamination