6 research outputs found
Ab initio studies of structures and properties of small potassium clusters
We have studied the structure and properties of potassium clusters containing
even number of atoms ranging from 2 to 20 at the ab initio level. The geometry
optimization calculations are performed using all-electron density functional
theory with gradient corrected exchange-correlation functional. Using these
optimized geometries we investigate the evolution of binding energy, ionization
potential, and static polarizability with the increasing size of the clusters.
The polarizabilities are calculated by employing Moller-Plesset perturbation
theory and time dependent density functional theory. The polarizabilities of
dimer and tetramer are also calculated by employing large basis set coupled
cluster theory with single and double excitations and perturbative triple
excitations. The time dependent density functional theory calculations of
polarizabilities are carried out with two different exchange-correlation
potentials: (i) an asymptotically correct model potential and (ii) within the
local density approximation. A systematic comparison with the other available
theoretical and experimental data for various properties of small potassium
clusters mentioned above has been performed. These comparisons reveal that both
the binding energy and the ionization potential obtained with gradient
corrected potential match quite well with the already published data.
Similarly, the polarizabilities obtained with Moller-Plesset perturbation
theory and with model potential are quite close to each other and also close to
experimental data.Comment: 33 pages including 10 figure
Whales, dolphins or fishes? The ethnotaxonomy of cetaceans in São Sebastião, Brazil
The local knowledge of human populations about the natural world has been addressed through ethnobiological studies, especially concerning resources uses and their management. Several criteria, such as morphology, ecology, behavior, utility and salience, have been used by local communities to classify plants and animals. Studies regarding fishers' knowledge on cetaceans in the world, especially in Brazil, began in the last decade. Our objective is to investigate the folk classification by fishers concerning cetaceans, and the contribution of fishers' local knowledge to the conservation of that group. In particular, we aim to record fishers' knowledge in relation to cetaceans, with emphasis on folk taxonomy. The studied area is São Sebastião, located in the southeastern coast of Brazil, where 70 fishers from 14 communities were selected according to their fishing experience and interviewed through questionnaires about classification, nomenclature and ecological aspects of local cetaceans' species. Our results indicated that most fishers classified cetaceans as belonging to the life-form 'fish'. Fishers' citations for the nomenclature of the 11 biological species (10 biological genera), resulted in 14 folk species (3 generic names). Fishers' taxonomy was influenced mostly by the phenotypic and cultural salience of the studied cetaceans. Cultural transmission, vertical and horizontal, was intimately linked to fishers' classification process. The most salient species, therefore well recognized and named, were those most often caught by gillnets, in addition to the biggest ones and those most exposed by media, through TV programs, which were watched and mentioned by fishers. Our results showed that fishers' ecological knowledge could be a valuable contribution to cetaceans' conservation, helping to determine areas and periods for their protection, indicating priority topics for research and participating in alternative management related to the gillnet fisheries