Stirring Unmagnetized Plasma

A new concept for spinning unmagnetized plasma is demonstrated experimentally. Plasma is confined by an axisymmetric multi-cusp magnetic field and biased cathodes are used to drive currents and impart a torque in the magnetized edge. Measurements show that flow viscously couples momentum from the magnetized edge (where the plasma viscosity is small) into the unmagnetized core (where the viscosity is large) and that the core rotates as a solid body. To be effective, collisional viscosity must overcome the ion-neutral drag due to charge exchange collisions

Exotic Species and Overgrazing Can Drive Declines in Grassland Biodiversity and Productivity

Plant species diversity has declined rapidly in grasslands, and it is poorly known how to establish and maintain diverse mixtures containing grasses, forbs, and legumes. Each of these groups can be important. For example, grasses and forbs can produce forage and increase resistance to weeds, and legumes can produce forage and maintain high fertility by fixing nitrogen. There is some evidence that exotic (introduced) plant species and changes in land use are contributing to declines in diversity. Exotic species could be causing declines in diversity in situations where they differ from native plant species in growth rates and other plant traits. However, previous studies were based on correlative data, and we have a poor understanding of whether exotic species themselves are causing direct declines in diversity, or if associated land use changes are causing the declines in diversity