Coupled thrust and vorticity dynamics during VRS

The focus is on the vortex ring state (VRS) observed at rapid descent rates. At VRS, the helical vortex filaments coming off the blades amalgamate around the rotor disk forming a vortex ring, which periodically detaches into the wake, causing extreme oscillations in thrust, with periods on the order of several tens of rotor revolutions. We discuss here the phase relation between the thrust cycle and vorticity distribution at the rotor disk. Maxima of the VRS thrust oscilla- tions correlate well with the maxima of circulation, enstrophy, and minima of enstrophy dispersion radius observed in the vicinity of the rotor disk

The BIOSIS data base: Evaluation of its indexes and the STRATBLDR, CHEMFILE, STAIRS and DIALOG systems for on-line searching

An IBM-developed program, STAIRS, was selected for performing a search on the BIOSIS file. The evaluation of the hardware and search systems and the strategies used are discussed. The searches are analyzed by type of end user

Shifting sands

The article presents the proposed changes to the New Zealand Draft Curriculum on the Nature of Science. In July 2006, the draft was released to school and the wider educational community for consultation on the national curriculum policy. It asserts to help science teachers to develop their understanding on nature of scientific knowledge and on how the community can effectively teach such aspects of the curriculum in the classroom setting

Comment on ''Properties of highly clustered networks"

We consider a procedure for generating clustered networks previously reported by Newman [Phys. Rev. E 68, 026121 (2003)]. In the same study, clustered networks generated according to the proposed model have been reported to have a lower epidemic threshold under susceptible-infective-recovered-type network epidemic dynamics. By rewiring networks generated by this model, such that the degree distribution is conserved, we show that the lower epidemic threshold can be closely reproduced by rewired networks with close to zero clustering. The reported lower epidemic threshold can be explained by different degree distributions observed in the networks corresponding to different levels of clustering. Clustering results in networks with high levels of heterogeneity in node degree, a higher proportion of nodes with zero connectivity, and links concentrated within highly interconnected components of small size. Hence, networks generated by this model differ in both clustering and degree distribution, and the lower epidemic threshold is not explained by clustering alone

Effects of deposit-feeding bivalve (Macomona liliana) density on intertidal sediment stability

Effects of macrofaunal feeding and bioturbation on intertidal sediment stability (u*crit) were investigated by manipulating density (0-3 x ambient) of the facultative deposit-feeding wedge shell (Macomona liliana) on the Tuapiro sandflat in Tauranga Harbour, New Zealand. Sediment stability increased up to 200% with decreasing M. liliana density and this was correlated with greater sediment microalgal biomass and mucilage content. The change in stability occurred despite homogeneity of grain size amongst experimental treatments, highlighting the importance of macrofaunal-microbial relationships in determining estuarine sediment erodibility

Observations of the Vortex Ring State

This paper considers the vortex ring state, a flow condition usually associated with the descent of a rotor into its own wake. The phenomenon is investigated through experiments on simple rotor systems, and a comparison is then made with observations of a flow generated by a specially designed open core, annular jet that generates a mean flow velocity profile similar to the mean flow in a rotor wake in hover. In an experimentally simulated descent, the jet flow generates a flow state that shares many features of the rotor vortex ring state