No abstract

<p>Este trabalho teve como objetivo ajustar e selecionar modelos matemáticos para a estimativa do volume comercial com casca para espécies comerciais de uma Floresta Ombrófila Densa de Terra Firme localizada no sul de Roraima. Foram abatidas e cubadas pelo método de Smalian 122 árvores de 18 espécies com diâmetro à altura do peito maior do que 50 cm. Foram testados nove modelos, ajustados pelos métodos dos mínimos quadrados, e selecionados em função do coeficiente de determinação ajustado, do erro padrão de estimativa em porcentagem, do valor de F calculado e da análise gráfica da distribuição dos resíduos. Recomendou-se o modelo de Schumacher-Hall. O modelo de Kopezki-Gherardt pode ser empregado, quando não se utilizar dados de altura comercial.</p>

This study investigates the problem of controller design for systems with uncertain sampling rates. The system is controlled through a communication network. The sampling period, within a given interval, is assumed to be time-varying and a simplified framework for the network-induced delay is considered. The overall system is thus described by an uncertain discrete-time model with time-varying parameters inside a polytope whose vertices are obtained by means of the Cayley-Hamilton theorem. A digital robust controller that minimises an upper bound to the H 1 performance of the closed-loop networked control system (NCS) is determined. The design conditions rely on a particular parameter-dependent Lyapunov function and are expressed as bilinear matrix inequalities (BMIs) in terms of extra matrix variables, which may be explored in the search for a better system behaviour. Numerical examples illustrate the results.

This paper provides finite dimensional convex conditions to construct homogeneous polynomially parameter-dependent Lur'e functions which ensure the stability of nonlinear systems with state-dependent nonlinearities lying in general sectors and which are affected by uncertain parameters belonging to the unit simplex. The proposed conditions are written as linear matrix inequalities parametrized in terms of the degree g of the parameterdependent solution and in terms of the relaxation level d of the inequality constraints, based on algebraic properties of positive matrix polynomials with parameters in the unit simplex. As g and d increase, progressively less conservative solutions are obtained. The results in the paper include as special cases existing conditions for robust stability and for absolute stability analysis. A convex solution suitable for the design of robust nonlinear state feedback stabilizing controllers is also provided. Numerical examples illustrate the efficiency of the proposed conditions.

In order to simulate the conditions of the space environment at ground, the Laboratory of Application and Innovation in Aerospace Science (LAICA) of the University of Brasília (UnB) is developing a dedicated testbed aiming at reproducing nanosatellite attitude motion. The testbed is composed of an air bearing table and a Helmholtz cage. The air bearing table is a spacecraft simulator that can simulate frictionless conditions with three rotational degrees of freedom. Balancing the simulator is essential in order to make the gravitational torque negligible. The testbed 1 Silva, Approved on June 18th, 2018 is also equipped with a Helmholtz cage whose purpose is to recreate the Earth magnetic field conditions that spacecrafts encounter in orbit. The design and realization of this low-cost testbed is presented in this paper. A simple and efficient automated balancing algorithm based on the Least Squares Method (LSM) is proposed and validated by experiments. The performance of the proposed simulator is evaluated and compared with previous works.