A geometric characterisation of the blocks of the Brauer algebra

We give a geometric description of the blocks of the Brauer algebra $B_n(\delta)$ in characteristic zero as orbits of the Weyl group of type $D_n$. We show how the corresponding affine Weyl group controls the representation theory of the Brauer algebra in positive characteristic, with orbits corresponding to unions of blocks.Comment: 26 pages, 24 figure

Wake length of an artificial seagrass meadow: a study of shelter and its feasibility for restoration

Seagrasses are essential marine ecosystems for which restoration has proven challenging due to increased hydrodynamic stress. This study aims to analyze the flow alteration induced by an artificial seagrass (ASG) meadow by characterizing its wake effect through a shelter distance and thus yield guidance for seagrass restoration projects. Here, we define shelter distance as the longitudinal extent behind a meadow, with respect to the flow direction, where seagrass is protected and can hence grow successfully. Flume experiments were conducted for submerged meadows with three different lengths at constant canopy height, shoot density and water depth, and three different cross-section-averaged longitudinal flow velocities measured with state-of-the-art Particle Image Velocimetry (PIV). For the tested meadow morphology and hydrodynamic conditions, meadow length played a less important role regarding shelter distance, while incident flow velocity and effective canopy height governed the wake effect. Incident velocities 2 m behind the meadow, whereas higher velocities led to a reduced shelter distance ranging from 20-40 cm. ASG additionally produced an upwelling effect on the vertical distribution of the velocity profile observed along the wake, regardless of meadow length and incident velocity. Our results suggest that restoration projects should aim for areas of low flow, where currents induced by tidal or wind waves are less pronounced in order to activate larger shelter distances

Flow field and wake structure characteristics imposed by single seagrass blade surrogates

Seagrass surrogates are commonly used to mimic the behaviour of seagrasses exposed to currents and their effects on flow fields. The interaction is highly dependent on the chosen mechanic and geometric properties of the surrogates and needs to be understood in order to design artificial meadows. The interaction of single surrogates in unidirectional flow fields is studied by means of physical modelling. Surrogates made of plastic materials with different flexural rigidities, buoyancies and geometries are exposed to varying flow velocities. The instantaneous velocity fields in the vicinity and wake of the surrogates are measured by stereoscopic Particle Image Velocimetry (PIV). All employed surrogates disrupt and interact with the flow field by changing their posture. An empirical relation is derived between the flexural rigidity, buoyancy and characteristic diameter of the surrogates and the imposed differences in the attenuation ratio of flow velocities. Further, the approaching flow velocity and distance behind the surrogate influence the estimated attenuation. The vortex shedding frequency imposed by artificial seagrass is lower than frequencies determined for infinite, rigid cylindrical structures. Three main characterizing properties: the modulus of elasticity, buoyancy and cross-sectional dimensions need to be taken into account for design of artificial seagrass meadows. Our findings advance knowledge of fluid-structure interactions of flexible materials and help to progress proper design of artificial seagrass meadows

Towards a territorial political capacity approach for studying European regions

This article proposes a framework for studying the territorial political capacity of regions in Europe. The proposed framework identifies three main dimensions of territorial political capacity. Mainly material indicators include institutions and institutional resources. Mixed material and constructed indicators centre on causal mechanisms of party and leadership capacity. Mainly constructed indicators are drawn from territorial praxis. Understanding a region requires combining different levels of analysis and distinctive ways of knowing; broad-based (quasi-statistical) variables facilitate comparison, while the focus on resilience and capacity requires primary data collection, drilling down into the practices of comparable panels of actors. This article discusses this framework in relation to four European regions that were the object of empirical investigation in 2012–2014: namely Brittany (France), Andalusia (Spain), Wallonia (Belgium) and Wales (United Kingdom). It contributes to the conceptualization of comparative territorial capacity, in a manner distinct from, but largely consistent with the Regional Authority Index

Acquisition and maintenance of excellence:the challenges faced by Dutch top-level gymnasts throughout different stages of athletic development

The purpose of the present study is to identify the within-career challenges top-level gymnasts experience during the initiation, development and mastery stage of athletic development in training sessions, competition, and in daily life. In-depth interviews are used to explore the perceived challenges of 16 talented and elite gymnasts (M = 16.5 years, SD = 4.6 years). Participants are divided into three groups, according to the stage of their athletic development. Several challenges are perceived in all stages of athletic development (e.g. learning new elements, dealing with stress under pressure, dealing with distractions and managing their dual career). As the number of different challenges increases as the gymnasts reach the mastery stage, challenges seem to become more personal and specific than in previous stages. The study shows obvious differences in the nature of the perceived challenges for different stages of athletic development, which provides useful insights for those who work with talented and elite athletes

On the blocks of the walled Brauer algebra

We determine the blocks of the walled Brauer algebra in characteristic zero. These can be described in terms of orbits of the action of a Weyl group of type $A$ on a certain set of weights. In positive characteristic we give a linkage principle in terms of orbits of the corresponding affine Weyl group. We also classify the semisimple walled Brauer algebras in all characteristics.Comment: 40 pages, 16 figure