Tunneling conductance in Superconductor/Ferromagnet junctions: a self consistent approach

We evaluate the tunneling conductance of clean Ferromomagnet/Superconductor junctions via a fully self-consistent numerical solution of the microscopic Bogoliubov-DeGennes equations. We present results for a relevant range of values of the Fermi wavevector mismatch (FWM), the spin polarization, and the interfacial scattering strength. For nonzero spin polarization, the conductance curves vary nonmonotonically with FWM. The FWM dependence of the self-consistent results is stronger than that previously found in non-self-consistent calculations, since, in the self-consistent case, the effective scattering potential near the interface depends on the FWM. The dependence on interfacial scattering is monotonic. These results confirm that it is impossible to characterize both the the FWM and the interfacial scattering by a single effective parameter and that analysis of experimental data via the use of such one-parameter models is unreliable.Comment: 12 pages, including 8 figure

Theory of pixel lensing towards M31 I: the density contribution and mass of MACHOs

POINT-AGAPE is an Anglo-French collaboration which is employing the Isaac Newton Telescope (INT) to conduct a pixel-lensing survey towards M31. In this paper we investigate what we can learn from pixel-lensing observables about the MACHO mass and fractional contribution in M31 and the Galaxy for the case of spherically-symmetric near-isothermal haloes. We employ detailed pixel-lensing simulations which include many of the factors which affect the observables. For a maximum MACHO halo we predict an event rate in V of up to 100 per season for M31 and 40 per season for the Galaxy. However, the Einstein radius crossing time is generally not measurable and the observed full-width half-maximum duration provides only a weak tracer of lens mass. Nonetheless, we find that the near-far asymmetry in the spatial distribution of M31 MACHOs provides significant information on their mass and density contribution. We present a likelihood estimator for measuring the fractional contribution and mass of both M31 and Galaxy MACHOs which permits an unbiased determination to be made of MACHO parameters, even from data-sets strongly contaminated by variable stars. If M31 does not have a significant population of MACHOs in the mass range 0.001-1 Solar masses strong limits will result from the first season of INT observations. Simulations based on currently favoured density and mass values indicate that, after three seasons, the M31 MACHO parameters should be constrained to within a factor four uncertainty in halo fraction and an order of magnitude uncertainty in mass (90% confidence). Interesting constraints on Galaxy MACHOs may also be possible. For a campaign lasting ten years, comparable to the lifetime of current LMC surveys, reliable estimates of MACHO parameters in both galaxies should be possible. (Abridged)Comment: 21 pages, 14 figures. Submitted to MNRA

Deforestation and wildlife management: are elephants attracted by recently deforested areas?

Deforestation is a major cause or wildlife decline in tropical ecosystems. The conversion of mature forest to fields by shifting cultivation leaves behind follow lands with secondary vegetation. Paradoxically, secondary forest regrowth that provides abundant forage in comparison with mature forests can benefit some species as the African elephant (Loxodonta africana) but they are also attracted towards human communities and cultivations raising conservation issues. The study was conducted in Gile National Reserve, Mozambique, an unfenced protected area composed of Miombo woodland. Among 60 elephants remaining in the Reserve, 5 individuals were equipped with GPS collars in 2014 in 2016. Deforestation was monitored by remote sensing from 1990 to 2016 and a map of forest productivity was built To test our hypothesis, we modelled resource selection functions using the GPS data. Elephants spend about half of their time in the core area and half in the buffer zone where most of the deforestation occurs. Elephants neither prefer nor avoid pristine forest habitats and cleared between 1990 and 2005. They prefer areas cleared since 2005 where forest regrowth occurred since 2009. The areas the most selected were cleared between 2010 and 2013 and were in cultivation during the study. Shifting agriculture leads to the displacement elephants toward cultivated fields and regenerating forest vegetation thus increasing Human/Elephant conflicts. This resource selection strategy also raises conservation questions related to the Reserve management aiming at reducing deforestation. Diversity of habitats should be maintained and resource selection linked to vegetation dynamics should be further understood