Simón Bolívar University

About: Simón Bolívar University is a education organization based out in Caracas, Venezuela. It is known for research contribution in the topics: Population & Crystallization. The organization has 5912 authors who have published 8294 publications receiving 126152 citations.

Simultaneous Contact, Gait and Motion Planning for Robust Multi-Legged Locomotion via Mixed-Integer Convex Optimization

Abstract: Traditional motion planning approaches for multilegged locomotion divide the problem into several stages, such as contact search and trajectory generation. However, reasoning about contacts and motions simultaneously is crucial for the generation of complex whole-body behaviors. Currently, coupling theses problems has required either the assumption of a fixed gait sequence and flat terrain condition, or nonconvex optimization with intractable computation time. In this letter, we propose a mixed-integer convex formulation to plan simultaneously contact locations, gait transitions, and motion, in a computationally efficient fashion. In contrast to previous works, our approach is not limited to flat terrain nor to a prespecified gait sequence. Instead, we incorporate the friction cone stability margin, approximate the robot's torque limits, and plan the gait using mixed-integer convex constraints. We experimentally validated our approach on the HyQ robot by traversing different challenging terrains, where nonconvexity and flat terrain assumptions might lead to suboptimal or unstable plans. Our method increases the motion robustness while keeping a low computation time.

General morphology, anatomical structure, and nutrient content of sclerophyllous leaves of the 'bana' vegetation of amazonas.

Abstract: Species of the ‘bana’ vegetation in the Amazonas region of equatorial South America have scleromorphic leaves. This leaf type, which characterizes the vegetation of Mediterranean climates, among others, has apparently evolved in this community in response to the oligotrophic soils and widely fluctuating water table. Anatomically, the leaves have several features commonly found in xeromorphic plants, including greater leaf and cuticle thickness, pubescent leaves and sunken stomata, and a high incidence of sclerenchyma. Concentrations of K and P decrease with leaf age, while N remains nearly constant and Ca increases. Concentrations of N and P are lower than in other sclerophyllous species, but the amount of these nutrients recovered before leaf shedding are similar. The correlation between P and N as expressed per unit dry weight is high (r=0.87; p 300 ppm) and Al (>1000 ppm).

Velocity field across the Southern Caribbean Plate Boundary and estimates of Caribbean/South‐American Plate Motion using GPS Geodesy 1994–2000

Abstract: Global Positioning System (GPS) observations between 1994 and 2000 at twenty-two sites in the Lesser Antilles and northern South-America indicate that the Caribbean plate, along its southern boundary, slips at a rate of 20.5±2 mm/a with an azimuth of N 84°±2°E at 65°W, relative to the South-American plate. East of 68° W, 80% of the dextral slip is contained within a 80-km wide shear zone centered on the El Pilar-San Sebastian fault system. West of 68° W the plate boundary broadens to more than 300 km with dextral shear shared between the northeast trending Bocono fault (9–11 mm/a) in western Venezuelan, and an offshore system near the northern coast.

Solving POMDPs: RTDP-bel vs. point-based algorithms

Abstract: Point-based algorithms and RTDP-Bel are approximate methods for solving POMDPs that replace the full updates of parallel value iteration by faster and more effective updates at selected beliefs. An important difference between the two methods is that the former adopt Sondik's representation of the value function, while the latter uses a tabular representation and a discretization function. The algorithms, however, have not been compared up to now, because they target different POMDPs: discounted POMDPs on the one hand, and Goal POMDPs on the other. In this paper, we bridge this representational gap, showing how to transform discounted POMDPs into Goal POMDPs, and use the transformation to compare RTDP-Bel with point-based algorithms over the existing discounted benchmarks. The results appear to contradict the conventional wisdom in the area showing that RTDP-Bel is competitive, and sometimes superior to point-based algorithms in both quality and time.

Fermi LAT Observations of Supernova Remnants Interacting with Molecular Clouds

Abstract: We report the detection of gamma-ray emission coincident with four supernova remnants (SNRs) using data from the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. G349.7+0.2, CTB 37A, 3C 391 and G8.7-0.1 are supernova remnants known to be interacting with molecular clouds, as evidenced by observations of hydroxyl (OH) maser emission at 1720 MHz in their directions. SNR shocks are expected to be sites of cosmic rays acceleration, and clouds of dense material can provide effective targets for production of gamma-rays from pion-decay. The observations reveal unresolved sources in the direction of G349.7+0.2, CTB 37A and 3C 391, and a possibly extended source coincident with G8.7-0.1, all with significance levels greater than 10 sigma.