Controle de atitude e altitude para um veículo aéreo não tripulado do tipo quadrirrotor

A Quadrotor is an Unmanned Aerial Vehicle (UAV) equipped with four rotors distributed on a simple mechanical "X"form structure. The aim of this work is to build and stabilize a Quadrotor aircraft in the roll, pitch and yaw angles at a certain altitude. The stabilization control approach is based on a transformation in the input variables in order to perform a decoupled control. The proposed strategy is based on breaking the control problem into two hierarchical levels: A lower level, object of this work, maintains the desired altitude an angles of the vehicle while the higher level establishes appropriate references to the lower level, performing the desired movements. A hardware and software architecture was specially developed and implemented for an experimental prototype used to test and validate the proposed control approach

Fases magnéticas de sistemas nanoestruturados de terras-raras

There is presently a worldwide interest in artificial magnetic systems which guide research activities in universities and companies. Thin films and multilayers have a central role, revealing new magnetic phases which often lead to breakthroughs and new technology standards, never thought otherwise. Surface and confinement effects cause large impact in the magnetic phases of magnetic materials with bulk spatially periodic patterns. New magnetic phases are expected to form in thin film thicknesses comparable to the length of the intrinsic bulk magnetic unit cell. Helimagnetic materials are prototypes in this respect, since the bulk magnetic phases consist in periodic patterns with the length of the helical pitch. In this thesis we study the magnetic phases of thin rare-earth films, with surfaces oriented along the (002) direction. The thesis includes the investigation of the magnetic phases of thin Dy and Ho films, as well as the thermal hysteresis cycles of Dy thin films. The investigation of the thermal hysteresis cycles of thin Dy films has been done in collaboration with the Laboratory of Magnetic Materials of the University of Texas, at Arlington. The theoretical modeling is based on a self-consistent theory developed by the Group of Magnetism of UFRN. Contributions from the first and second neighbors exchange energy, from the anisotropy energy and the Zeeman energy are calculated in a set of nonequivalent magnetic ions, and the equilibrium magnetic phases, from the Curie temperature up to the Nèel temperature, are determined in a self-consistent manner, resulting in a vanishing torque in the magnetic ions at all planes across the thin film. Our results reproduce the known isothermal and iso-field curves of bulk Dy and Ho, and the known spin-slip phases of Ho, and indicate that: (i) the confinement in thin films leads to a new magnetic phase, with alternate helicity, which leads to the measured thermal hysteresis of Dy ultrathin films, with thicknesses ranging from 4 nm to 16 nm; (ii) thin Dy films have anisotropy dominated surface lock-in phases, with alignment of surface spins along the anisotropy easy axis directions, similar to the known spin-slip phases of Ho ( which form in the bulk and are commensurate to the crystal lattice); and (iii) the confinement in thin films change considerably the spin-slip patterns of Ho.

Avaliando o impacto da utilização de renderizações panorâmicas para a navegação em ambientes virtuais

Panoramic rendering is the visualization of three-dimensional objects in a virtual environment through a wide viewing angle. This work investigated if the use of panoramas is able to promote faster searches in a virtual environment. Panoramas allow the presentation of space through less need to change the orientation of the camera, especially for the case of projections spanning 360º surrounding the user, which can benefit searching. However, the larger the angle, more distorted is the visualization of the environment, causing confusion in navigation. The distortion is even bigger when the user changes the pitch of the camera, by looking up or down. In this work we developed a technique to eliminate specifically the distortions caused by changes in pitch, which was called hemispheric projection. Experiments were done to evaluate the performance of search navigation through perspective, cylindrical and hemispherical projections. The results indicate that navigating with perspective projection is superior than navigating with panoramic projections, possibly due to factors such as (i) lack of experience of the participants in understanding the scenes displayed as panoramas, (ii) the inherent presence of distortion in panoramic projections and (iii) a lower display resolution because the objects are presented in smaller sizes in panoramic projections, making the perception of details more difficult. However, the hemispherical projection was better than the cylindrical, indicating that the developed technique provides benefits for navigation compared to current techniques of panoramic projection. The hemispheric projection also provided the least amount of changes of camera orientation, which is an indication that the hemispheric projections may be particularly useful in situations where there are restrictions on the ease to change the orientation. Future research will investigate the performance of cameras interactions on slower devices, such as using only keyboard, or brain-machine interfaces

Explorando a execução de técnicas estendidas no oboé encontradas em quatro peças contemporâneas

This dissertation presents an investigation of the evolutionary process of extended oboe techniques, through literary analysis and practical research. The objective of this work is to provide assistance to oboists interested in learning these techniques. Additionally, this work encourages the student, through the process of experimentation, to explore the questions that may arise around the aesthetics of sound, the concept of gesture as an additional visual and aural element in music, and the collaboration and “real-time” creation processes. Discussed within the work, are the relationship between the instrument (the oboe) and extended techniques, and two possible definitions of extended techniques, provided by Luk Vaes (2009) and Gardner Read (1993). Also explored are the how and why some composers have utilized extended techniques in their compositions, including brief discussions relating to extended techniques in real-time composition (improvisation), extended techniques and technological resources, theatrical gesture as an extended technique, and suggestions of how musicians might approach theatrical gestures in performance. Four works were visited: “I Know This Room So Well” – Lisa Bielawa (2007-9); “Four Pieces for Oboe and Piano” – Ernst Krenek (1966); “In Freundschaft” – Karlheinz Stockhausen (1978); “Atem” – Mauricio Kagel (1969-70); and an exploration of the difficulties and solutions associated with each extended technique found within these pieces, was carried out. The following founding works on extended oboe techniques were used, as a basis for research: books - Heinz Holliger’s Pro Musica Nova (1972); Gardner Read’s Compendium of Modern Instrumental Techniques (1993); Peter Veale & Claus-Steffen Mahnkopf’s The Techniques of Oboe Playing (1994); and Libby Van Cleve’s Oboe Unbound: Contemporary Techniques (2004); and articles - Nora Post’s “Monophonic sound resources for the oboe: Part I – Timbre” (1984), “Part II- Pitch and other techniques” (1984), and “Multiphonics for the oboe” (1982).