Jairo Mojica

Devonian plants from Colombia, with discussion of their geological and palaeogeographical context

Plant fossils are described from the Cuche Formation, Eastern Cordillera, Colombia in the area of Floresta. Those identified as Colpodexylon cf. deatsii Banks and cf. Archaeopteris sp. suggest an earliest Late Devonian (Frasnian) age for the formation. These or similar taxa are also found in contemporaneous deposits in western Venezuela, and other elements of the Venezuelan flora are found in a geographically intermediate locality. All three Devonian plant localities in the northwest of South America are within the Colombian Eastern Cordillera and its northern extension, the Venezuelan Perija Range, an area that has been integrated as a part of the so-called ‘Eastern Andean Terrane’ or ‘Central Andean Province’, supposedly accreted to the autochthonous block of the Guyana Shield during the early Jurassic or before. Although both invertebrates and plants from this terrane have strong affinities to North American and European assemblages, and might be interpreted as implying a Laurussian origin for the Eastern Andean Terrane, the evidence is not yet unequivocal, with some authors postulating an in situ development of this province.

Page clustering using a distance based algorithm

This paper presents an application of a clustering algorithm based on gravitational forces to the problem of Web page clustering in a dynamic environment. The proposed algorithm uses a modification of the gravitational algorithm proposed by Gomez et al. but using only the distance measures (a notion of space is not required). This approach is useful when similarities (and/or then distances) between pages can be defined and compute quickly, but the definition of a space is computationally expensive. Experiments with data representing real URLs and sessions are performed, and a comparison with the incremental connected components algorithm, which has been previously used to solve this problem, is done.