Theory of Transmission through disordered superlattices

We derive a theory for transmission through disordered finite superlattices in which the interface roughness scattering is treated by disorder averaging. This procedure permits efficient calculation of the transmission thr ough samples with large cross-sections. These calculations can be performed utilizing either the Keldysh or the Landauer-B\"uttiker transmission formalisms, both of which yield identical equations. For energies close to the lowest miniband, we demonstrate the accuracy of the computationally efficient Wannier-function approximation. Our calculations indicate that the transmission is strongly affected by interface roughness and that information about scale and size of the imperfections can be obtained from transmission data.Comment: 12 pages, 6 Figures included into the text. Final version with minor changes. Accepted by Physical Review

Population predictions for Seychelles warblers in novel environments.

A major challenge for population ecology is to be able to predict population sizes in novel conditions, as in those following habitat loss or translocation. To do this successfully, we show here that it is necessary to understand the behavioral basis of dispersal decisions as they affect fitness. The Seychelles warbler, like many socially complex species, lives in family groups. This leads to the stable usage of sink habitats through kin competition. Sink usage means that bird density is not representative of habitat quality, and consequently that simple extrapolations from current habitat occupancy mis-estimate the effects of habitat loss. Similarly, per territory reproductive success for Seychelles warblers declines with density within a habitat class, in common with many territorial species. This too undermines the use of simple extrapolations to predict the consequences of habitat loss. Retrospective predictions for two actual translocations show some success, while the extent to which they fail emphasizes the need for full understanding of the links between the environment occupied and reproductive success.