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Itacoatiara, Brazil

Carrera D.H.Z.,ita | Weber H.I.,Pontifical Catholic University of Rio de Janeiro
AIP Conference Proceedings | Year: 2012

The goal of this work is the investigation of the necessary conditions for the possible existence of tumbling in rotational motion of rigid bodies. In a stable spinning satellite, tumbling may occur by sufficient strong action of external impulses, when the conical movement characteristic of the stable attitude is de-characterized. For this purpose a methodology is chosen to simplify the study of rotational motions with great amplitude, for example free bodies in space, allowing an extension of the analysis to non-conservative systems. In the case of a satellite in space, the projection of the angular velocity along the principal axes of inertia must be known, defining completely the initial conditions of motion for stability investigations. In this paper, the coordinate systems are established according to the initial condition in order to allow a simple analytical work on the equations of motion. Also it will be proposed the definition of a parameter, calling it tumbling coefficient, to measure the intensity of the tumbling and the amplitude of the motion when crossing limits of stability in the concept of Lyapunov. Tumbling in the motion of bodies in space is not possible when this coefficient is positive. Magnus Triangle representation will be used to represent the geometry of the body, establishing regions of stability/instability for possible initial conditions of motion. In the study of nonconservative systems for an oblate body, one sufficient condition will be enough to assure damped motion, and this condition is checked for a motion damped by viscous torques. This paper seeks to highlight the physical understanding of the phenomena and the influence of various parameters that are important in the process. © 2012 American Institute of Physics. Source

Chagas T.P.,State University of Santa Cruz | Bliman P.-A.,French Institute for Research in Computer Science and Automation | Kienitz K.H.,ita
Proceedings of the IEEE Conference on Decision and Control | Year: 2012

This work presents a new method of stabilization for unstable periodic orbits of continuous-time dynamical systems. The principle of this method is to use feedback term based on the difference between the actual state value and the future state value computed along the trajectories of the uncontrolled system. To compute the value of the latter, an implicit Runge-Kutta ODE integration method is used, giving rise to a time-varying dynamical controller. The stability of the control method is defined in terms of the Floquet theory and the conditions for calculation of the monodromy matrix are presented. Numerical results are obtained using the forced Van der Pol oscillator as case study and the orthogonal collocation method as implicit Runge-Kutta method. © 2012 IEEE. Source

Moreira G.S.P.,Ci and T | Souza G.,Ci and T | Da Cunha A.M.,ita
CEUR Workshop Proceedings | Year: 2015

In this investigation, we conduct a comparison between offine and online accuracy evaluation of different algorithms and settings in a real-world content recommender system. By focusing on recommendations of long-tail items, which are usually more interesting for users, it was possible to reduce the bias caused by extremely popular items and to observe a better alignment of accuracy results in offine and online evaluations. Source

Merlin B.,University Paul Sabatier | Hiirata C.,ita
Proceedings of the SBSC 2010 - 7th Brazilian Symposium on Collaborative Systems | Year: 2010

Collaborative systems are used in several application areas. But, in the context of critical activities, where human life may be involved, the acceptation of such a system substituting human-human coordination is more difficult. The user must delegate a part of his responsibilities to the system and must have a high level of trust in its. Moreover it is difficult to promote changes in an implanted system leading to an evolution of working methods. This article tackles an experience of a collaborative system development in the context of the French air traffic control. We observe that the main artifact of coordination (the paper strip) between air traffic controllers turned an obstacle to the modernization of the system and to a wider collaboration. We searched an alternative to substitute the strip paper and a process to gain the trust of the user in the new system. The article relates the project experience and highlight recommendation for the development of these systems in critical activity contexts. © 2010 IEEE. Source

Vieira B.,Aeronautics Institute of Technology ITA | Junior W.S.,ita
Ambiente e Sociedade | Year: 2015

Advances in water management require knowledge of the availability and demand of water resources to define priority actions for water conservation. The aim of this study is to support the development of municipal initiatives involving Water Footprint, based on a case study of Caraguatatuba, using 2012 data. The following water footprints were considered: a) the urban water system; b) sewage production; c) cattle-farming; and d) rural water uses. Results showed water footprint levels of approximately 400 Mm3/year, where grey water represents the largest share (85%). Furthermore, results showed that the increased pressure on local water resources results from the disparity between the sewage system in relation to the demands of a growing population. This study can contribute to improve Water Footprint methodology, promoting comparative studies and supporting water management policies in this socio-political field. Source

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