Geometrically nonlinear bending analysis of functionally graded beam with variable thickness by a meshless method
COMPOSITE STRUCTURES
Authors: Lin, Jun; Li, Jiao; Guan, Yanjin; Zhao, Guoqun; Naceur, Hakim; Coutellier, Daniel
Abstract
Geometrically nonlinear bending deformation of Functionally Graded Beams (FGBs) with variable thickness is simulated by a meshless Smoothed Hydrodynamic Particle (SPH) method. The material properties of FGB is assumed to be varied smoothly in the thickness according to exponent-law distribution. To prevent themesh-distortion in element-based numerical method, meshless SPH method is adopted, where corrective smoothed particle method and total-Lagrangian formulation are employed to improve its precision and stability. To validate the present SPH method, several numerical examples are performed and compared to analytical and finite element solutions.
Molecular systematics and biogeography of lowland antpittas (Aves, Grallariidae): The role of vicariance and dispersal in the diversification of a widespread Neotropical lineage
MOLECULAR PHYLOGENETICS AND EVOLUTION
Authors: Carneiro, Lincoln; Bravo, Gustavo A.; Aristizabal, Natalia; Cuervo, Andres M.; Aleixo, Alexandre
Abstract
We infer phylogenetic relationships, divergence times, and the diversification history of the avian Neotropical antpitta genera Hylopezus and Myrmothera (Grallariidae), based on sequence data (3,139 base pairs) from two mitochondrial (ND2 and ND3) and three nuclear nuclear introns (TGFB2, MUSK and FGB-I5) from 142 individuals of the 12 currently recognized species in Hylopezus and Myrmothera and 5 outgroup species. Phylogenetic analyses recovered 19 lineages clustered into two major clades, both distributed in Central and South America. Hylopezus nattereri, previously considered a subspecies of H. ochroleucus, was consistently recovered as the most divergent lineage within the Grallaricula/Hylopezus/Myrmothera clade. Ancestral range estimation suggested that modern lowland antpittas probably originated in the Amazonian Sedimentary basin during the middle Miocene, and that most lineages within the Hylopezus/Myrmothera clade appeared in the Plio-Pleistocene. However, the rate of diversification in the Hylopezus/Myrmothera clade appeared to have remained constant through time, with no major shifts over the 20 million years. Although the timing when most modern lineages of the Hylopezus/Myrmothera clade coincides with a period of intense landscape changes in the Neotropics (Plio-Pleistocene), the absence of any significant shifts in diversification rates over the last 20 million years challenges the view that there is a strict causal relationship between intensification of landscape changes and cladogenesis. The relative old age of the Hylopezus/Myrmothera clade coupled with an important role ascribed to dispersal for its diversification, favor an alternative scenario whereby long-term persistence and dispersal across an ever-changing landscape might explain constant rates of cladogenesis through time.