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Publicações

2024

Improving constraints on the extended mass distribution in the Galactic center with stellar orbits

Autores
Abd El Dayem, K; GRAVITY Collaboration; Abuter, R; Aimar, N; Seoane, PA; Amorim, A; Beck, J; Berger, JP; Bonnet, H; Bourdarot, G; Brandner, W; Cardoso, V; Dolcetta, RC; Clénet, Y; Davies, R; de Zeeuw, PT; Drescher, A; Eckart, A; Eisenhauer, F; Feuchtgruber, H; Finger, G; Schreiber, NMF; Foschi, A; Gao, F; Garcia, P; Gendron, E; Genzel, R; Gillessen, S; Hartl, M; Haubois, X; Haussmann, F; Heissel, G; Henning, T; Hippler, S; Horrobin, M; Jochum, L; Jocou, L; Kaufer, A; Kervella, P; Lacour, S; Lapeyrère, V; Le Bouquin, JB; Léna, P; Lutz, D; Mang, F; More, N; Ott, T; Paumard, T; Perraut, K; Perrin, G; Pfuhl, O; Rabien, S; Ribeiro, DC; Bordoni, MS; Scheithauer, S; Shangguan, J; Shimizu, T; Stadler, J; Straub, O; Straubmeier, C; Sturm, E; Tacconi, LJ; Urso, I; Vincent, F; von Fellenberg, SD; Widmann, F; Wieprecht, E; Woillez, J; Zhang, F;

Publicação
ASTRONOMY & ASTROPHYSICS

Abstract
Studying the orbital motion of stars around Sagittarius A* in the Galactic center provides a unique opportunity to probe the gravitational potential near the supermassive black hole at the heart of our Galaxy. Interferometric data obtained with the GRAVITY instrument at the Very Large Telescope Interferometer (VLTI) since 2016 has allowed us to achieve unprecedented precision in tracking the orbits of these stars. GRAVITY data have been key to detecting the in-plane, prograde Schwarzschild precession of the orbit of the star S2 that is predicted by general relativity. By combining astrometric and spectroscopic data from multiple stars, including S2, S29, S38, and S55 - for which we have data around their time of pericenter passage with GRAVITY - we can now strengthen the significance of this detection to an approximately 10 sigma confidence level. The prograde precession of S2's orbit provides valuable insights into the potential presence of an extended mass distribution surrounding Sagittarius A*, which could consist of a dynamically relaxed stellar cusp comprising old stars and stellar remnants, along with a possible dark matter spike. Our analysis, based on two plausible density profiles - a power-law and a Plummer profile - constrains the enclosed mass within the orbit of S2 to be consistent with zero, establishing an upper limit of approximately 1200 M-circle dot with a 1 sigma confidence level. This significantly improves our constraints on the mass distribution in the Galactic center. Our upper limit is very close to the expected value from numerical simulations for a stellar cusp in the Galactic center, leaving little room for a significant enhancement of dark matter density near Sagittarius A*.

2024

A Community-Driven Data-to-Text Platform for Football Match Summaries

Autores
Fernandes, P; Nunes, S; Santos, L;

Publicação
Proceedings of the 2024 Joint International Conference on Computational Linguistics, Language Resources and Evaluation, LREC/COLING 2024, 20-25 May, 2024, Torino, Italy.

Abstract
Data-to-text systems offer a transformative approach to generating textual content in data-rich environments. This paper describes the architecture and deployment of Prosebot, a community-driven data-to-text platform tailored for generating textual summaries of football matches derived from match statistics. The system enhances the visibility of lower-tier matches, traditionally accessible only through data tables. Prosebot uses a template-based Natural Language Generation (NLG) module to generate initial drafts, which are subsequently refined by the reading community. Comprehensive evaluations, encompassing both human-mediated and automated assessments, were conducted to assess the system's efficacy. Analysis of the community-edited texts reveals that significant segments of the initial automated drafts are retained, suggesting their high quality and acceptance by the collaborators. Preliminary surveys conducted among platform users highlight a predominantly positive reception within the community.

2024

Multi-Agent Reinforcement Learning for Side-by-Side Navigation of Autonomous Wheelchairs

Autores
Fonseca, T; Leao, G; Ferreira, LL; Sousa, A; Severino, R; Reis, LP;

Publicação
2024 IEEE INTERNATIONAL CONFERENCE ON AUTONOMOUS ROBOT SYSTEMS AND COMPETITIONS, ICARSC

Abstract
This paper explores the use of Robotics and decentralized Multi-Agent Reinforcement Learning (MARL) for side-by-side navigation in Intelligent Wheelchairs (IW). Evolving from a previous work approach using traditional single-agent methodologies, it adopts a Multi-Agent Deep Deterministic Policy Gradient (MADDPG) algorithm to provide control input and enable a pair of IW to be deployed as decentralized computing agents in real-world environments, discarding the need to rely on communication between each other. In this study, the Flatland 2D simulator, in conjunction with the Robot Operating System (ROS), is used as a realistic environment to train and test the navigation algorithm. An overhaul of the reward function is introduced, which now provides individual rewards for each agent and revised reward incentives. Additionally, the logic for identifying side-by-side navigation was improved, to encourage dynamic alignment control. The preliminary results outline a promising research direction, with the IWs learning to navigate in various realistic hallways testing scenarios. The outcome also suggests that while the MADDPG approach holds potential over single-agent techniques for the decentralized IW robotics application, further investigation are needed for real-world deployment.

2024

Comparative Analysis of TLS and UAV Sensors for Estimation of Grapevine Geometric Parameters

Autores
Ferreira, L; Sousa, JJ; Lourenço, JM; Peres, E; Morais, R; Pádua, L;

Publicação
SENSORS

Abstract
Understanding geometric and biophysical characteristics is essential for determining grapevine vigor and improving input management and automation in viticulture. This study compares point cloud data obtained from a Terrestrial Laser Scanner (TLS) and various UAV sensors including multispectral, panchromatic, Thermal Infrared (TIR), RGB, and LiDAR data, to estimate geometric parameters of grapevines. Descriptive statistics, linear correlations, significance using the F-test of overall significance, and box plots were used for analysis. The results indicate that 3D point clouds from these sensors can accurately estimate maximum grapevine height, projected area, and volume, though with varying degrees of accuracy. The TLS data showed the highest correlation with grapevine height (r = 0.95, p < 0.001; R2 = 0.90; RMSE = 0.027 m), while point cloud data from panchromatic, RGB, and multispectral sensors also performed well, closely matching TLS and measured values (r > 0.83, p < 0.001; R2 > 0.70; RMSE < 0.084 m). In contrast, TIR point cloud data performed poorly in estimating grapevine height (r = 0.76, p < 0.001; R2 = 0.58; RMSE = 0.147 m) and projected area (r = 0.82, p < 0.001; R2 = 0.66; RMSE = 0.165 m). The greater variability observed in projected area and volume from UAV sensors is related to the low point density associated with spatial resolution. These findings are valuable for both researchers and winegrowers, as they support the optimization of TLS and UAV sensors for precision viticulture, providing a basis for further research and helping farmers select appropriate technologies for crop monitoring.

2024

Estimating Completeness of Consensus Models: Geometrical and Distributional Approaches

Autores
Strecht, P; Moreira, JM; Soares, C;

Publicação
Machine Learning, Optimization, and Data Science - 10th International Conference, LOD 2024, Castiglione della Pescaia, Italy, September 22-25, 2024, Revised Selected Papers, Part I

Abstract
In many organizations with a distributed operation, not only is data collection distributed, but models are also developed and deployed separately. Understanding the combined knowledge of all the local models may be important and challenging, especially in the case of a large number of models. The automated development of consensus models, which aggregate multiple models into a single one, involves several challenges, including fidelity (ensuring that aggregation does not penalize the predictive performance severely) and completeness (ensuring that the consensus model covers the same space as the local models). In this paper, we address the latter, proposing two measures for geometrical and distributional completeness. The first quantifies the proportion of the decision space that is covered by a model, while the second takes into account the concentration of the data that is covered by the model. The use of these measures is illustrated in a real-world example of academic management, as well as four publicly available datasets. The results indicate that distributional completeness in the deployed models is consistently higher than geometrical completeness. Although consensus models tend to be geometrically incomplete, distributional completeness reveals that they cover the regions of the decision space with a higher concentration of data. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2025.

2024

First Resolution of Microlensed Images of a Binary-lens Event

Autores
Wu, ZX; Dong, SB; Merand, A; Kochanek, CS; Mróz, P; Shangguan, JY; Christie, G; Tan, TG; Bensby, T; Bland-Hawthorn, J; Buder, S; Eisenhauer, F; Gould, AP; Kos, J; Natusch, T; Sharma, S; Udalski, A; Woillez, J; Buckley, DAH; Thompson, IB; El Dayem, KA; Berdeu, A; Berger, JP; Bourdarot, G; Brandner, W; Davies, RI; Defrère, D; Dougados, C; Drescher, A; Eckart, A; Fabricius, M; Feuchtgruber, H; Schreiber, NMF; Garcia, P; Genzel, R; Gillessen, S; Heissel, G; Hönig, S; Houlle, M; Kervella, P; Kreidberg, L; Lacour, S; Lai, O; Laugier, R; Le Bouquin, JB; Leftley, J; Lopez, B; Lutz, D; Mang, F; Millour, F; Montargès, M; Nowacki, H; Nowak, M; Ott, T; Paumard, T; Perraut, K; Perrin, G; Petrov, R; Petrucci, PO; Pourre, N; Rabien, S; Ribeiro, DC; Robbe-Dubois, S; Bordoni, MS; Santos, D; Sauter, J; Scigliuto, J; Shimizu, TT; Straubmeier, C; Sturm, E; Subroweit, M; Sykes, C; Tacconi, L; Vincent, F; Widmann, F; GRAVITY Collaboration;

Publicação
ASTROPHYSICAL JOURNAL

Abstract
We resolve the multiple images of the binary-lens microlensing event ASASSN-22av using the GRAVITY instrument of the Very Large Telescope Interferometer (VLTI). The light curves show weak binary-lens perturbations, complicating the analysis, but the joint modeling with the VLTI data breaks several degeneracies, arriving at a strongly favored solution. Thanks to precise measurements of the angular Einstein radius theta E = 0.724 +/- 0.002 mas and microlens parallax, we determine that the lens system consists of two M dwarfs with masses of M 1 = 0.258 +/- 0.008 M circle dot and M 2 = 0.130 +/- 0.007 M circle dot, a projected separation of r perpendicular to = 6.83 +/- 0.31 au, and a distance of D L = 2.29 +/- 0.08 kpc. The successful VLTI observations of ASASSN-22av open up a new path for studying intermediate-separation (i.e., a few astronomical units) stellar-mass binaries, including those containing dark compact objects such as neutron stars and stellar-mass black holes.

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