Dusty plasma cavities: probe-induced and natural

A comprehensive exploration of regional dust evacuation in complex plasma crystals is presented. Voids created in 3D crystals on the International Space Station have provided a rich foundation for experiments, but cavities in dust crystals formed in ground-based experiments have not received as much attention. Inside a modified GEC RF cell, a powered vertical probe was used to clear the central area of a dust crystal, producing a cavity with high cylindrical symmetry. Cavities generated by three mechanisms are examined. First, repulsion of micrometer-sized particles by a negatively charged probe is investigated. A model of this effect developed for a DC plasma is modified and applied to explain new experimental data in RF plasma. Second, the formation of natural cavities is surveyed; a radial ion drag proposed to occur due to a curved sheath is considered in conjunction with thermophoresis and a flattened confinement potential above the center of the electrode. Finally, cavity formation unexpectedly occurs upon increasing the probe potential above the plasma floating potential. The cavities produced by these methods appear similar, but each are shown to be facilitated by fundamentally different processes.Comment: 10 pages, 12 figure

Foot-and-Mouth Disease control costs compared: An Irish case study.

The primary objective of this paper is to evaluate alternative control strategies for a number of simulated outbreaks of Foot-and-Mouth Disease (FMD) in four agriculturally diverse Irish regions, examining for the first time, the potential role of emergency vaccination in the country. The recent EU Directive (2003/85/EC) on FMD control permits the use of emergency vaccination as part of an FMD control strategy. While the slaughter of infected animals and dangerous contacts (susceptible animals on epidemiologically linked holdings) remains the principal tool for tackling an outbreak, the potential use of vaccination as an adjunct to the basic culling policy is now being considered. Using an integrated approach, combining epidemiological and economic modules, the alternatives of stamping-out both alone and in conjunction with emergency vaccination are examined using hypothetical outbreaks and their control costs compared. Overall, it cannot be said, a priori, that one control option is better than the other. Choice of control strategy would appear to be highly dependent on herd density, production type and other region specific issues. This analysis has focused on control costs only; taking wider economy costs into account may however change this overall conclusion.Foot-and-Mouth disease, alternative control strategies, transboundary animal diseases, emergency vaccination, Livestock Production/Industries, Q1, Q17, Q58,