The use of multibeam sonar mapping techniques to refine population estimates of the endangered white abalone (Haliotis sorenseni)

Multibeam sonar mapping techniques provide detailed benthic habitat information that can be combined with the data on species-specific habitat preferences to provide highly accurate calculations of populations in a particular area. The amount of suitable habitat available for the endangered white abalone (Haliotis sorenseni) was quantified to aid in obtaining an accurate estimate of the number of remaining individuals at two offshore banks and one island site off the coast of southern California. Habitat was mapped by using multibeam sonar survey techniques and categorized by using rugosity and topographic position analysis. Abalone densities were evaluated by using a remotely operated vehicle and video transect methods. The total amount of suitable habitat at these three sites was far greater than that previously estimated. Therefore, although present estimates of white abalone densities are several orders of magnitude lower than historic estimates, the total population is likely larger than previously reported because of the additional amount of habitat surveyed in this study.

Double proximity effect in lateral S-NF-S junctions

We investigate planar Josephson junctions where the intermediate spacer between the two superconductors is an hybrid structure made by a normal metal and a ferromagnet. The different behaviors of the S-N-S junctions with thicknesses of 50 nm in both Cu and Nb layers, and S-N/F-S junctions with 10 nm of Co, 50 nm of Cu and 50 nm of Nb are studied. In this way, we analyze the influence of the ferromagnetic exchange interaction on the proximity effect. A dramatic supression of the josephson critical current of the Nb-(Cu/Co)-Nb junctions is observed. We believe that the reason for this is due to the length scale of the superconducting correlations of the electrons and holes of the weak link is larger than the thickness of Cu/Co bilayer.