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Publicações

2013

Multi-Robot Cooperative Stereo for Outdoor Scenarios

Autores
Dias, A; Almeida, J; Silva, E; Lima, P;

Publicação
PROCEEDINGS OF THE 2013 13TH INTERNATIONAL CONFERENCE ON AUTONOMOUS ROBOT SYSTEMS (ROBOTICA)

Abstract
In this paper, we propose a cooperative perception framework for multi-robot real-time 3D high dynamic target estimation in outdoor scenarios based on monocular camera available on each robot. The relative position and orientation between robots establishes a flexible and dynamic stereo baseline. Overlap views subject to geometric constraints emerged from the stereo formulation, which allowed us to obtain a decentralized cooperative perception layer. Epipolar constraints related to the global frame are applied both in image feature matching and to feature searching and detection optimization in the image processing of robots with low computational capabilities. In contrast to classic stereo, the proposed framework considers all sources of uncertainty (in localization, attitude and image detection from both robots) in the determination of the objects best 3D localization and its uncertainty. The proposed framework can be later integrated in a decentralized data fusion (DDF) multi-target tracking approach where it can contribute to reduce rumor propagation data association and track initialization issues. We demonstrate the advantages of this approach in real outdoor scenario. This is done by comparing a stereo rigid baseline standalone target tracking with the proposed multi-robot cooperative stereo between a micro aerial vehicle (MAV) and an autonomous ground vehicle (AGV).

2013

The impact of time in link-based Web ranking

Autores
Nunes, S; Ribeiro, C; David, G;

Publicação
INFORMATION RESEARCH-AN INTERNATIONAL ELECTRONIC JOURNAL

Abstract
Introduction. The strong dynamic nature of the Web is a well-known reality. Nonetheless, research on Web dynamics is still a minor part of mainstream Web research. This is largely the case in Web link analysis. In this paper we investigate and measure the impact of time in link-based ranking algorithms on a particular subset of the Web, specifically blogs. Method. Using a large collection of blog posts that span more than three years, we compare a traditional link-based ranking algorithm with a time-biased alternative, providing some insights into the evolution of link data over time. We designed two experiments to evaluate the use of temporal features in authority estimation algorithms. In the first experiment we compare time-independent and time-sensitive ranking algorithms with a reference rank based on the total number of visits to each blog. In the second, we use feedback from communication media domain experts to contrast different rankings of Portuguese news Websites. Results. The distribution of citations to a Web document over time contains valuable information. Based on several examples we show that time-independent algorithms are unable to capture the correct popularity of sites with high citation activity. Using a reference rank based on the number of visits to a site, we show that a time-biased approach has a better performance. Conclusions. Although both time-independent and time-aware approaches are based on the same raw data, the experiments indicate that they can be treated as complementary signals for relevance assessment by information retrieval systems. We show that temporal information present in blogs can be used to derive stable time-dependent features, which can be successfully used in the context of Web document ranking.

2013

Revisiting transactions in Ada

Autores
Barros, A; Pinho, LM;

Publicação
ACM SIGAda Ada Letters

Abstract
Classical lock-based concurrency control does not scale with current and foreseen multi-core architectures, opening space for alternative concurrency control mechanisms. The concept of transactions executing concurrently in isolation with an underlying mechanism maintaining a consistent system state was already explored in fault-tolerant and distributed systems, and is currently being explored by transactional memory, this time being used to manage concurrent memory access. In this paper we discuss the use of Software Transactional Memory (STM), and how Ada can provide support for it. Furthermore, we draft a general programming interface to transactional memory, supporting future implementations of STM oriented to real-time systems.

2013

Influence of Diffusion Parameters on the Spectral Characteristics of Raman Modes of Titanium-Diffused Lithium Niobate Planar Waveguides

Autores
de Almeida, JMMM; Agostinho Moreira, JA;

Publicação
SPECTROSCOPY LETTERS

Abstract
A systematic investigation on the influence of the diffusion parameters (time and temperature) and initial titanium film thickness on the spectral characteristics of the LiNbO3 Raman modes is reported. Raman spectra are measured in the range 501000cm(1)approximate to 2 mu m below the surface of the crystals. Broadening of the Raman lines and, therefore, crystal lattice disorder induced by the titanium ions are found to depend on the fabrication parameters. The disorder associated with the titanium ions near the surface of LiNbO3 is encoded in the broadening of the A(1)(TO1) Raman line. A linear relation between the A(1)(TO1) mode broadening and the Ti concentration is presented. The diffusion theory is used to explain the experimental data. Raman spectroscopy combined with diffusion theory can be used to estimate the evolution of the titanium surface concentration.

2013

Immune response is a personal matter

Autores
Ferreira, PG; Dermitzakis, ET;

Publicação
eLife

Abstract

2013

Designing User Learning Experience in Virtual Worlds: The Young Europeans for Democracy Serious Application

Autores
Cruz, G; Maia, A; Morgado, L; Fonseca, B; Paredes, H; Bessa, F; Rodrigues, C; Martins, P;

Publicação
ADVANCES IN INFORMATION SYSTEMS AND TECHNOLOGIES

Abstract
In this paper, we present the user experience design of Young Europeans for Democracy (YED) serious application. Facing the actually need to support young citizens understanding and participation in Europe, schools have a key role on European studies integration. Accordingly to the growing opportunities of applying technology for training and education, we propose a serious application in a open-source 3D Virtual World environment solution, adopting a problem-based learning approach, role-playing dynamics and group work tasks. The main goal was to design a meaningfully user experience, increasing the students motivation and engagement for learning different knowledge on the topics of European Studies. Some preliminary results are presented, based on participatory observation within the use of the serious application.

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