Optimal On-Off Attitude Control for the Brazilian Multimission Platform Satellite

This work deals with the analysis and design of a reaction thruster attitude control for the Brazilian Multimission platform satellite. The three-axis attitude control systems are activated in pulse mode. Consequently, a modulation of the torque command is compelling in order to avoid high nonlinear control action. This work considers the Pulse-Width Pulse-Frequency (PWPF) modulator which is composed of a Schmidt trigger, a first-order filter, and a feedback loop. PWPF modulator holds several advantages over classical bang-bang controllers such as close to linear operation, high accuracy, and reduced propellant consumption. The Linear Gaussian Quadratic (LQG) technique is used to synthesize the control law during stabilization mode and the modulator is used to modulate the continuous control signal to discrete one. Numerical simulations are used to analyze the performance of the attitude control. The LQG/PWPF approach achieves good stabilization-mode requirements as disturbances rejection and regulation performance

Variabilidade entre isolados de Trichoderma spp. quanto à capacidade de inibir o crescimento de Cylindrocladium sp. em cultivo pareado.

bitstream/CENARGEN/29462/1/bp186.pd

Cobb's collar and chronic renal failure

Pontificia Univ Catolica Campinas, Campinas, SP, BrazilUniv Fed Sao Paulo, Sao Paulo, SP, BrazilUniv Fed Sao Paulo, Sao Paulo, SP, BrazilWeb of Scienc

Forward scattering amplitudes in the imaginary time formalism

We study, in the imaginary time formalism, the relation between loops and on-shell forward scattering tree amplitudes in thermal field theories. This allows for an efficient evaluation, at all temperatures, of Green's functions with causal retarded boundary conditions. We present an application of this relation in quantum gravity coupled to scalar matter fields. We show that at one or two loops, involving planar diagrams, the 1PI retarded thermal Green's functions may respectively be expressed in terms of connected forward scattering tree amplitudes of one or two on-shell particles.Comment: 15 pages, four figures. Published in Physical Review D (typos corrected

Thermal gauge theories with Lagrange multiplier fields

We study the Yang-Mills theory and quantum gravity at finite temperature, in the presence of Lagrange multiplier fields. These restrict the path integrals to field configurations which obey the classical equations of motion. This has the effect of doubling the usual one--loop thermal contributions and of suppressing all radiative corrections at higher loop order. Such theories are renormalizable at all temperatures. Some consequences of this result in quantum gravity are briefly examined.Comment: 8 pages, 4 figures. To appear in the Canadian Journal of Physics (typos corrected