Obstacle avoidance strategy based on adaptive potential fields generated by an electronic stick

In our previous work, an obstacle avoidance algorithm, which used potential fields and a similar strategy to that adopted by a blind person to avoid obstacles whilst walking, was proposed. The problem analyzed consists of an AGV (Autonomous Guided Vehicle) which moves within an office environment with a known floor plan and uses an ”electronic stick” made up of infrared sensors to detect unknown obstacles in its path. Initially, a global potential navigation function, defined for each room in the floor plan, incorporates information about the dimensions of the room and the position of the door which the AGV must use to leave the room. Whilst the AGV moves, this global potential navigation function is properly modified to incorporate information about any newly detected obstacle. The main interesting aspect of the proposed approach is that the potential function adaptation involves very low computational burden allowing for the use of Ultra-fast AGVs. Other distinctive features of the algorithm are that it is free from local minima, the obstacles can have any shape, low cost sensors can be used to detect obstacles and an appropriate balance is achieved between the use of the global and the local approaches for collision avoidance. Our present work is a refinement of this strategy that allows for an automatic real time adaptation of the algorithm’s parameters. Now, the algorithm’s functioning requires only that the minimum distance at which the AGV can approach an obstacle (i.e. the closest it can get to any obstacle) is defined a priori. Aspects of the real implementation of the algorithm are also discussed

Door crossing and state identification using robotic vision

This project is aimed at the implementation of an autonomous vehicle guide (AGV) to navigate in internal environments, such as hospitals, offices, residences and so on. The work presents a new 3D algorithm for robotic vision, used for automatic identification of the state of doors, without any previous information about the environment, such as maps, location of obstacles, illumination and the like. The characteristics of the doors that would influence the decision of the robot on the identification of its state, also not ignored, such as texture, color, dimensions. Published in the 8th IFAC International Sysmposium on Robot Control (SYROCO 2006), this work presented the application of the Hougth Transform in images captured by the robotic vision. The coordinates of Hougth then presented the location of the edges of the doors and the analysis of cross-corelation of the found ones, gave us the configuration of the state of the door (open, closed, half open). With the results obtained, the navigation of the autonomous robot became more secure, since the risks of collision were minimized. Navigation using 3D vision, with real-time processing, also reduced the risk of collision with objects dynamically positioned in the environment. In the first part of this document, we present the article published in (SYROCO 2006). In the second part, we present some of the experimental results obtained during the project.O presente relatório técnico trata de um dos projetos realizados no Laboratório de Controle – CONTROLAB do Núcleo de Computação Eletrônica – NCE da Universidade Federal do Rio de Janeiro – UFRJ, nos anos de 2004 e 2005. Este projeto é voltado para a implementação de um robô autônomo AGV (Autonomous Vehicle Guide) para navegar em ambientes internos, tais como hospitais, escritórios, residências e etc. Especializado na área de visão computacional, O trabalho apresenta um novo algoritmo 3D para visão robótica, utilizado para identificação automática do estado de portas, sem quaisquer informações prévias sobre o ambiente, tais como mapas, localização de obstáculos, iluminação e etc. As próprias características das portas que influenciariam na decisão do robô sobre a identificação de seu estado, também não ignoradas, tais como textura, cor, dimensões. Publicado no 8th IFAC International Sysmposium on Robot Control (SYROCO 2006), o trabalho apresentou a aplicação da Transformada de Hougth em imagens capturada pela visão robótica. As coordenadas de Hougth apresentavam então a localização das arestas das portas e a análise de corelação cruzada das quinas encontradas, nos davam a configuração do estado da porta (aberta, fechada, entre-aberta). Com os resultados obtidos, a navegação do robô autônomo se tornava mais segura, vez que os riscos de colisão eram minimizados. A navegação utilizando visão 3D, com processamento em tempo real, também reduzia o risco de colisão com objetos dinamicamente posicionados no ambiente. Na primeira parte deste documento, apresentamos o artigo publicado em (SYROCO 2006). Na segunda parte, apresentamos alguns dos resultados experimentais obtidos durante a realização do projeto

Notas sobre visualização

Neste trabalho é apresentado uma exposição dos conceitos teóricos da computação gráfica referentes às transformações geométricas, a projeção e a iluminação que permitem a visualização das cenas. E dada uma breve explanação de como a biblioteca gráfica OpenGL implementa esses conceitos

Curvas e superfícies

Este trabalho apresenta uma exposição dos conceitos teóricos da computação gráfica referente às curvas e superfícies. Inicialmente é feita uma apresentação da conceituação de curvas e superfícies da geometria e da geometria diferencial e em seguida discute-se a adaptação destes conceitos às necessidades da computação gráfica. Mais precisamente, são apresentadas as diversas formas de representação das curvas e superfícies como curvas e superfícies paramétricas polinomiais por partes

Measurement of the cosmic ray spectrum above 4×10184{\times}10^{18} eV using inclined events detected with the Pierre Auger Observatory

A measurement of the cosmic-ray spectrum for energies exceeding $4{\times}10^{18}$ eV is presented, which is based on the analysis of showers with zenith angles greater than $60^{\circ}$ detected with the Pierre Auger Observatory between 1 January 2004 and 31 December 2013. The measured spectrum confirms a flux suppression at the highest energies. Above $5.3{\times}10^{18}$ eV, the "ankle", the flux can be described by a power law $E^{-\gamma}$ with index $\gamma=2.70 \pm 0.02 \,\text{(stat)} \pm 0.1\,\text{(sys)}$ followed by a smooth suppression region. For the energy ($E_\text{s}$) at which the spectral flux has fallen to one-half of its extrapolated value in the absence of suppression, we find $E_\text{s}=(5.12\pm0.25\,\text{(stat)}^{+1.0}_{-1.2}\,\text{(sys)}){\times}10^{19}$ eV.Comment: Replaced with published version. Added journal reference and DO

Energy Estimation of Cosmic Rays with the Engineering Radio Array of the Pierre Auger Observatory

The Auger Engineering Radio Array (AERA) is part of the Pierre Auger Observatory and is used to detect the radio emission of cosmic-ray air showers. These observations are compared to the data of the surface detector stations of the Observatory, which provide well-calibrated information on the cosmic-ray energies and arrival directions. The response of the radio stations in the 30 to 80 MHz regime has been thoroughly calibrated to enable the reconstruction of the incoming electric field. For the latter, the energy deposit per area is determined from the radio pulses at each observer position and is interpolated using a two-dimensional function that takes into account signal asymmetries due to interference between the geomagnetic and charge-excess emission components. The spatial integral over the signal distribution gives a direct measurement of the energy transferred from the primary cosmic ray into radio emission in the AERA frequency range. We measure 15.8 MeV of radiation energy for a 1 EeV air shower arriving perpendicularly to the geomagnetic field. This radiation energy -- corrected for geometrical effects -- is used as a cosmic-ray energy estimator. Performing an absolute energy calibration against the surface-detector information, we observe that this radio-energy estimator scales quadratically with the cosmic-ray energy as expected for coherent emission. We find an energy resolution of the radio reconstruction of 22% for the data set and 17% for a high-quality subset containing only events with at least five radio stations with signal.Comment: Replaced with published version. Added journal reference and DO

Measurement of the Radiation Energy in the Radio Signal of Extensive Air Showers as a Universal Estimator of Cosmic-Ray Energy

We measure the energy emitted by extensive air showers in the form of radio emission in the frequency range from 30 to 80 MHz. Exploiting the accurate energy scale of the Pierre Auger Observatory, we obtain a radiation energy of 15.8 \pm 0.7 (stat) \pm 6.7 (sys) MeV for cosmic rays with an energy of 1 EeV arriving perpendicularly to a geomagnetic field of 0.24 G, scaling quadratically with the cosmic-ray energy. A comparison with predictions from state-of-the-art first-principle calculations shows agreement with our measurement. The radiation energy provides direct access to the calorimetric energy in the electromagnetic cascade of extensive air showers. Comparison with our result thus allows the direct calibration of any cosmic-ray radio detector against the well-established energy scale of the Pierre Auger Observatory.Comment: Replaced with published version. Added journal reference and DOI. Supplemental material in the ancillary file

Consistent patterns of common species across tropical tree communities

Trees structure the Earth’s most biodiverse ecosystem, tropical forests. The vast number of tree species presents a formidable challenge to understanding these forests, including their response to environmental change, as very little is known about most tropical tree species. A focus on the common species may circumvent this challenge. Here we investigate abundance patterns of common tree species using inventory data on 1,003,805 trees with trunk diameters of at least 10 cm across 1,568 locations1,2,3,4,5,6 in closed-canopy, structurally intact old-growth tropical forests in Africa, Amazonia and Southeast Asia. We estimate that 2.2%, 2.2% and 2.3% of species comprise 50% of the tropical trees in these regions, respectively. Extrapolating across all closed-canopy tropical forests, we estimate that just 1,053 species comprise half of Earth’s 800 billion tropical trees with trunk diameters of at least 10 cm. Despite differing biogeographic, climatic and anthropogenic histories7, we find notably consistent patterns of common species and species abundance distributions across the continents. This suggests that fundamental mechanisms of tree community assembly may apply to all tropical forests. Resampling analyses show that the most common species are likely to belong to a manageable list of known species, enabling targeted efforts to understand their ecology. Although they do not detract from the importance of rare species, our results open new opportunities to understand the world’s most diverse forests, including modelling their response to environmental change, by focusing on the common species that constitute the majority of their trees.Publisher PDFPeer reviewe

Differential cross section measurements for the production of a W boson in association with jets in proton–proton collisions at √s = 7 TeV

Measurements are reported of differential cross sections for the production of a W boson, which decays into a muon and a neutrino, in association with jets, as a function of several variables, including the transverse momenta (pT) and pseudorapidities of the four leading jets, the scalar sum of jet transverse momenta (HT), and the difference in azimuthal angle between the directions of each jet and the muon. The data sample of pp collisions at a centre-of-mass energy of 7 TeV was collected with the CMS detector at the LHC and corresponds to an integrated luminosity of 5.0 fb[superscript −1]. The measured cross sections are compared to predictions from Monte Carlo generators, MadGraph + pythia and sherpa, and to next-to-leading-order calculations from BlackHat + sherpa. The differential cross sections are found to be in agreement with the predictions, apart from the pT distributions of the leading jets at high pT values, the distributions of the HT at high-HT and low jet multiplicity, and the distribution of the difference in azimuthal angle between the leading jet and the muon at low values.United States. Dept. of EnergyNational Science Foundation (U.S.)Alfred P. Sloan Foundatio