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Global warming has led to a strong deterioration of the Arctic sea ice cover. Ice thickness, age and coverage have been strongly declining in recent years. Brine channels that form in sea ice when seawater freezes represent a unique habitat for bacteria, algae, proto- and small metazoans. We hypothesized that the loss of multi-year ice and the more prevalent formation of first-year ice even in central regions of the Arctic will lead to changes in the Arctic sea ice meiofauna community composition. We therefore analysed the sea ice meiofauna community composition of three different ice types sampled in summer and autumn 2007. Young, thin ice of few cm thickness was typified by taxa of pelagic origin or with good swimming abilities (ciliates, pelagic foraminifera, rotifers and platyhelminthes). Harpacticoid copepods and nematodes with poor swimming abilities were prevalent in older, thicker (>0.5 m) first- and multi-year ice. Brash ice-which was likely a mix of older broken ice, slush and pancake ice-was characterized by a high abundance of platyhelminthes and rotifers. An experimental analysis of colonization efficiencies of artificial thin ice also revealed that species with poor swimming ability are less successful to colonize newly forming thin ice. We conclude that observed and predicted changes in the ice formation regime will likely result in changes in the composition of Arctic sea ice communities. We predict negative effects particularly for species with low dispersal capacities like harpacticoid copepods and endemic nematodes, as these are less successful in colonizing newly forming thin ice. [ABSTRACT FROM AUTHOR]

We present the coupling of a vortex particle-mesh method with immersed lifting lines for the Large Eddy Simulation of wind turbine wakes. The method relies on the Lagrangian discretization of the Navier–Stokes equations in vorticity-velocity formulation. Advection is handled by the particles while the mesh allows the evaluation of the differential operators and the use of fast Poisson solvers. We use a Fourier-based fast Poisson solver which simultaneously allows unbounded directions and inlet/outlet boundaries. The method also allows the feeding of a turbulent incoming flow. We apply this methodology to the study of large scale aerodynamics and wake behavior of tandem wind turbines. We analyze the generators performance, unsteady power, loads and aerodynamics they are subjected to. The average flow field of the wakes is also computed and turbulence statistics are extracted. In particular, we investigate the influence of the type of turbulent inflow used—precomputed or synthetic—, and study wake meandering. [ABSTRACT FROM AUTHOR]

10 MW, 140 GHz ECH system is currently under construction for the stellarator W7-X. The RF power will be provided by 10 gyrotrons. A European collaboration has been established to develop and build 9 (out of 10) tubes each with an output power of 1 MW for continuous wave (CW) operation. This contribution reports on recent results with the series gyrotrons. [ABSTRACT FROM AUTHOR]

The effect of RF-space charge fields on the beam-field interaction in gyrotrons is reviewed. This effect, formerly considered unimportant, is found to cause recognisable differences in simulations of gyrotrons with high current density, such as today's megawatt level gyrotrons. In this paper, a numerically efficient way of including RF-space charge in the common slow variables model is derived and numerical examples are presented. [ABSTRACT FROM AUTHOR]