douglas alves

Os seis ensaios do mais recente livro de Rodrigo Duarte — nome que se confunde com a recepção de Theodor W. Adorno no Brasil — apresentam aos leitores um exercício de reflexão sobre o lugar da dialética no horizonte filosófico contemporâneo. Trata-se de explicitar a ...

With the growing in the use of UAVs (Unmanned Aerial Vehicles), it is necessary to develop techniques that allow the generation of feasible paths for these vehicles. These paths take into account the nonholonomic constraints intrinsic to UAVs, such as minimum curvature, minimum torsion and maximum climb (or dive) angle. Thus, this paper proposes the use of genetic algorithms to generate paths for these vehicles in the three-dimensional space, using Bézier curves with several advantages. We consider all these three constraints in order to generate a feasible path for a small fixed-wing aircraft with severe limitations. We show results for this vehicle.

This paper presents a methodology based on a variation of the Rapidly-exploring Random Trees (RRTs) that generates feasible trajectories for autonomous aerial vehicles with holonomic constraints in environments with obstacles. Our approach uses Pythagorean Hodograph (PH) curves to connect vertices of the tree, which makes it possible to generate paths for which the main kinematic constraints of the vehicle are not violated. The smoothness of the acceleration profile of the vehicle is indirectly guaranteed between two vertices of the RRT tree. The proposed algorithm provides fast convergence to the final trajectory. We still utilize the properties of the RRT to avoid collisions with static obstacles of a environment. We show results for a small unmanned aerial vehicles in environments with different configurations.

The main purpose of this study was to provide an estimate for the onset of morphological sexual maturity in the freshwater crab Trichodactylus fluviatilis, from a population located in south-eastern Brazil, based on the relative growth relationships, as well as the characterization of “handedness”. Monthly collections were carried out at night, from January 2006 to January 2007, in a small water body. In the laboratory, the crabs were sexed; the following body structures were measured and the estimate of onset of sexual maturity was given by the logistic function, as y = a/(1 + be − cx), for 50% of the population to reach the adult phase (CW50carapace width). Right propodus length and abdomen width were the best-fit relationships to represent the onset of sexual maturity for males and females, respectively. Based on the logistic function, the onset of sexual maturity was estimated to occur at around 18 mm CW for both sexes. The relative growth recorded for this species is consistent with the model for brachyuran crabs (Hartnoll RG. 1982, Growth. In: Bliss, DE, editor. The biology of Crustacea: embryology, morphology and genetics. New York: Academic Press. p. 111–196), except for the abdomen growth, which is likely to be an adaptive condition related to protection of the newly hatched young.

Investigations of the distribution of marine organisms provide a better understanding of the patterns of distribution and dispersal of these animals. Extensions of the distributional limits of decapod crustaceans in Brazilian waters have been recorded steadily and gradually, but these limits still remain poorly understood. The present study provides information extending the known range of eight species of brachyuran crabs and one species of porcellanid crab. The animals were obtained by Scuba diving during a sampling program carried out near Vitória Island, Ilhabela, on the northeastern coast of the State of São Paulo (23º44'04"S-45º01'35"W) between February, 2004 and January, 2005. These new records extend the geographical distributions of the porcellanid Petrolisthes amoenus (Guérin Menéville, 1855), the majoids Mithrax caribbaeus Rathbun, 1920, Mithrax verrucosus H. Milne Edwards, 1832, Nemausa acuticornis (Stimpson, 1871) and Teleophrys ornatus Rathbun, 1901, and the xanthoids Domecia acanthophora acanthophora (Desbonne & Schramm, 1867), Garthiope spinipes (A. Milne Edwards, 1880), Xanthodius denticulatus (White, 1847) and Xanthodius parvulus (Fabricius, 1793) to the São Paulo coast. These new records may be related to different mechanisms of larval dispersal, larval transport by ballast water, or may simply be exceptional records.