OSIRIS (Optical System for Imaging and low Resolution Integrated Spectroscopy) is the optical Day One instrument for the 10.4m Spanish telescope GTC to be installed in the Observatorio del Roque de Los Muchachos (La Palma, Spain). This instrument, operational in mid-2004, covers from 360 up to 1000 nm. OSIRIS observing modes include direct imaging with tunable and conventional filters, long slit and multiple object spectroscopy and fast spectrophotometry. The OSIRIS wide field of view, high efficiency and the new observing modes (tunable imaging and fast spectrophotometry) for 8-10m class telescopes will provide GTC with a powerful tool for their scientific exploitation. The present paper provides an updated overview of the instrument development, of some of the scientific projects that will be tackled with OSIRIS and of the general requirements driving the optical and mechanical design.

There is much controversy about the minimum number of implants and maximum cantilever length in mandible prosthetic restoration. Finite elements analysis of three and four implant-supported prostheses was performed to determine the stresses in the superstructure, implants and cortical bone and, therefore, the failure prediction for each restoration. An edentulous mandible was modeled from CT scan images. Two finite element models of three and four implant-supported prostheses with cantilever lengths of 10 and 15 mm were created. Occlusal loads in different parts of the superstructure were applied and shear and normal stresses were calculated. Two failure criteria were analyzed: the von Mises criterion for isotropic materials (superstructure and implants) and the Tsai-Wu criterion for transversely isotropic material (cortical bone). Both criteria predict failure in the three implant-supported prosthesis for all cases analyzed. The same applies for the four-implant prosthesis of 15 mm cantilever length. However, four implants and a cantilever length of 10mm passed the failure criteria and were considered safe. The results from the patient analyzed showed that fixed support prostheses on three implants are not recommended from a structural point of view because they do not adequately support occlusal loads. Excessive stress in the superstructure and the cortical bone can be expected, which would anticipate the failure of the restoration. Fixed support prostheses on four implants with a cantilever length of 10mm properly resist occlusal loading.

Caiman crocodilus is an alligatoroid broadly distributed in the neotropics from Mexico to Brazil, where Colombia is the only country that has the complete subspecies complex distributed in its territory. This species has been the focus of many genetic, ecological and morphological studies. However, these studies are limited to traditional morphology methods or have limitations to examine interspecific variation among the four subspecies reported in Colombia. This is the first study of intraspecific variation in the skull of Caiman crocodilus complex distributed in Colombia, using a two-dimensional approach of geometric morphometric on 122 post-hatching ontogenetic cranial series. Morphological differences between species and changes during ontogeny (snout increases its length and, skull roof and orbits decrease their proportions) that represents part of morphological changes in the cranial ontogeny of crocodilians were found. In the morphospace, there was a significant differentiation of C. crocodilus apaporiensis and C. crocodilus crocodilus from C. crocodilus fuscus and C. crocodilus chiapasius. Results from this study revealed that C. crocodilus apaporiensis is a differentiated group from the global complex as well as that the specimens of C. crocodilus chiapasius collected from Medem in Colombia may be showing cryptic morphology in some traits.