Observation comparative du déplacement ionique dans les couches minces de PbF2 β et de CaF2 par diffusion Rutherford

Des couches minces de PbF2 β et de CaF2, dont les conductivités ioniques sont très différentes, ont été analysées par rétro-diffusion de particules α. On a pu observer, dans le cas de PbF2, une variation importante du rapport des concentrations fluor/plomb dans l'épaisseur de la couche, correspondant à une accumulation de fluor du côté du faisceau incident. Cet effet est atténué dans les couches de CaF2. L'interprétation des résultats est basée sur l'existence d'un nombre important de défauts créés par le faisceau, et sur leur déplacement sous l'effet de la charge superficielle due à l'émission secondaire d'électrons

O cultivo do tomate em Roraima.

bitstream/item/175139/1/0062002-tomate-joaci.pd

DNA Fingerprinting Validates Seed Dispersal Curves from Observational Studies in the Neotropical Legume Parkia

Background: Determining the distances over which seeds are dispersed is a crucial component for examining spatial patterns of seed dispersal and their consequences for plant reproductive success and population structure. However, following the fate of individual seeds after removal from the source tree till deposition at a distant place is generally extremely difficult. Here we provide a comparison of observationally and genetically determined seed dispersal distances and dispersal curves in a Neotropical animal-plant system. Methodology/Principal Findings: In a field study on the dispersal of seeds of three Parkia (Fabaceae) species by two Neotropical primate species, Saguinus fuscicollis and Saguinus mystax, in Peruvian Amazonia, we observationally determined dispersal distances. These dispersal distances were then validated through DNA fingerprinting, by matching DNA from the maternally derived seed coat to DNA from potential source trees. We found that dispersal distances are strongly rightskewed, and that distributions obtained through observational and genetic methods and fitted distributions do not differ significantly from each other. Conclusions/Significance: Our study showed that seed dispersal distances can be reliably estimated through observational methods when a strict criterion for inclusion of seeds is observed. Furthermore, dispersal distances produced by the two primate species indicated that these primates fulfil one of the criteria for efficient seed dispersers. Finally, our stud