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Publications

2024

The cool brown dwarf Gliese 229 B is a close binary

Authors
Xuan, JW; Mérand, A; Thompson, W; Zhang, Y; Lacour, S; Blakely, D; Mawet, D; Oppenheimer, R; Kammerer, J; Batygin, K; Sanghi, A; Wang, J; Ruffio, JB; Liu, MC; Knutson, H; Brandner, W; Burgasser, A; Rickman, E; Bowens-Rubin, R; Salama, M; Balmer, W; Blunt, S; Bourdarot, G; Caselli, P; Chauvin, G; Davies, R; Drescher, A; Eckart, A; Eisenhauer, F; Fabricius, M; Feuchtgruber, H; Finger, G; Schreiber, NMF; Garcia, P; Genzel, R; Gillessen, S; Grant, S; Hartl, M; Haussmann, F; Henning, T; Hinkley, S; Hönig, SF; Horrobin, M; Houllé, M; Janson, M; Kervella, P; Kral, Q; Kreidberg, L; Le Bouquin, JB; Lutz, D; Mang, F; Marleau, GD; Millour, F; More, N; Nowak, M; Ott, T; Otten, G; Paumard, T; Rabien, S; Rau, C; Ribeiro, DC; Bordoni, MS; Sauter, J; Shangguan, J; Shimizu, TT; Sykes, C; Soulain, A; Spezzano, S; Straubmeier, C; Stolker, T; Sturm, E; Subroweit, M; Tacconi, LJ; van Dishoeck, EF; Vigan, A; Widmann, F; Wieprecht, E; Winterhalder, TO; Woillez, J;

Publication
NATURE

Abstract
Owing to their similarities with giant exoplanets, brown dwarf companions of stars provide insights into the fundamental processes of planet formation and evolution. From their orbits, several brown dwarf companions are found to be more massive than theoretical predictions given their luminosities and the ages of their host stars1-3. Either the theory is incomplete or these objects are not single entities. For example, they could be two brown dwarfs each with a lower mass and intrinsic luminosity1,4. The most problematic example is Gliese 229 B (refs. 5,6), which is at least 2-6 times less luminous than model predictions given its dynamical mass of 71.4 +/- 0.6 Jupiter masses (MJup) (ref. 1). We observed Gliese 229 B with the GRAVITY interferometer and, separately, the CRIRES+ spectrograph at the Very Large Telescope. Both sets of observations independently resolve Gliese 229 B into two components, Gliese 229 Ba and Bb, settling the conflict between theory and observations. The two objects have a flux ratio of 0.47 +/- 0.03 at a wavelength of 2 mu m and masses of 38.1 +/- 1.0 and 34.4 +/- 1.5 MJup, respectively. They orbit each other every 12.1 days with a semimajor axis of 0.042 astronomical units (au). The discovery of Gliese 229 BaBb, each only a few times more massive than the most massive planets, and separated by 16 times the Earth-moon distance, raises new questions about the formation and prevalence of tight binary brown dwarfs around stars. Analysis of the cool brown dwarf Gliese 229 B suggests that it is actually a close binary of two less massive brown dwarfs, explaining its low luminosity and settling the conflict between theoretical predictions and measurements.

2024

Image Captioning for Coronary Artery Disease Diagnosis

Authors
Magalhaes, B; Pedrosa, J; Renna, F; Paredes, H; Filipe, V;

Publication
2024 IEEE INTERNATIONAL CONFERENCE ON BIOINFORMATICS AND BIOMEDICINE, BIBM

Abstract
Coronary artery disease (CAD) remains a leading cause of morbidity and mortality worldwide, underscoring the need for accurate and reliable diagnostic tools. While AI- driven models have shown significant promise in identifying CAD through imaging techniques, their 'black box' nature often hinders clinical adoption due to a lack of interpretability. In response, this paper proposes a novel approach to image captioning specifically tailored for CAD diagnosis, aimed at enhancing the transparency and usability of AI systems. Utilizing the COCA dataset, which comprises gated coronary CT images along with Ground Truth (GT) segmentation annotations, we introduce a hybrid model architecture that combines a Vision Transformer (ViT) for feature extraction with a Generative Pretrained Transformer (GPT) for generating clinically relevant textual descriptions. This work builds on a previously developed 3D Convolutional Neural Network (CNN) for coronary artery segmentation, leveraging its accurate delineations of calcified regions as critical inputs to the captioning process. By incorporating these segmentation outputs, our approach not only focuses on accurately identifying and describing calcified regions within the coronary arteries but also ensures that the generated captions are clinically meaningful and reflective of key diagnostic features such as location, severity, and artery involvement. This methodology provides medical practitioners with clear, context-rich explanations of AI-generated findings, thereby bridging the gap between advanced AI technologies and practical clinical applications. Furthermore, our work underscores the critical role of Explainable AI (XAI) in fostering trust, improving decision- making, and enhancing the efficacy of AI-driven diagnostics, paving the way for future advancements in the field.

2024

13th Symposium on Languages, Applications and Technologies, SLATE 2024, July 4-5, 2024, Águeda, Portugal

Authors
Rodrigues, M; Leal, JP; Portela, F;

Publication
SLATE

Abstract
[No abstract available]

2024

Exciting Surface Plasmon Resonances on Gold Thin Film-Coated Optical Fibers Through Nanoparticle Light Scattering

Authors
Mendes, JP; dos Santos, PSS; Dias, B; Núñez Sánchez, S; Pastoriza Santos, I; Pérez Juste, J; Pereira, CM; Jorge, PAS; de Almeida, JMMM; Coelho, LCC;

Publication
ADVANCED OPTICAL MATERIALS

Abstract
Surface plasmon resonance (SPR) conventionally occurs at the interface of a thin metallic film and an external dielectric medium in fiber optics through core-guided light. However, this work introduces theoretical and experimental evidence suggesting that the SPR in optical fibers can also be induced through light scattering from Au nanoparticles (NPs) on the thin metallic film, defined as nanoparticle-induced SPR (NPI-SPR). This method adheres to phase-matching conditions between SPR dispersion curves and the wave vectors of scattered light from Au NPs. Experimentally, these conditions are met on an etched optical fiber, enabling direct interaction between light and immobilized Au NPs. Compared to SPR, NPI-SPR exhibits stronger field intensity in the external region and wavelength tuning capabilities (750 to 1250 nm) by varying Au NP diameters (20 to 90 nm). NPI-SPR demonstrates refractive index sensitivities of 4000 to 4416 nm per refractive index unit, nearly double those of typical SPR using the same optical fiber configuration sans Au NPs. Additionally, NPI-SPR fiber configuration has demonstrated its applicability for developing biosensors, achieving a remarkable limit of detection of 0.004 nm for thrombin protein evaluation, a twenty-fold enhancement compared to typical SPR. These findings underscore the intrinsic advantages of NPI-SPR for sensing. Surface plasmon resonance (SPR) typically occurs at the interface of a thin metallic film and a dielectric medium in fiber optics. This work presents evidence of nanoparticle-induced SPR (NPI-SPR) in optical fibers through light scattering from Au nanoparticles on the thin metallic film. NPI-SPR offers stronger field intensity, wavelength tuning, and enhanced refractive index sensitivities, making it advantageous for biosensing applications. image

2024

The use of AI in government and its risks: lessons from the private sector

Authors
Santos, R; Brandao, A; Veloso, B; Popoli, P;

Publication
TRANSFORMING GOVERNMENT- PEOPLE PROCESS AND POLICY

Abstract
PurposeThis study aims to understand the perceived emotions of human-artificial intelligence (AI) interactions in the private sector. Moreover, this research discusses the transferability of these lessons to the public sector.Design/methodology/approachThis research analysed the comments posted between June 2022 and June 2023 in the global open Reddit online community. A data mining approach was conducted, including a sentiment analysis technique and a qualitative approach.FindingsThe results show a prevalence of positive emotions. In addition, a pertinent percentage of negative emotions were found, such as hate, anger and frustration, due to human-AI interactions.Practical implicationsThe insights from human-AI interactions in the private sector can be transferred to the governmental sector to leverage organisational performance, governmental decision-making, public service delivery and the creation of economic and social value.Originality/valueBeyond the positive impacts of AI in government strategies, implementing AI can elicit negative emotions in users and potentially negatively impact the brand of private and government organisations. To the best of the authors' knowledge, this is the first research bridging the gap by identifying the predominant negative emotions after a human-AI interaction.

2024

Towards Evaluation of Explainable Artificial Intelligence in Streaming Data

Authors
Mozolewski, M; Bobek, S; Ribeiro, RP; Nalepa, GJ; Gama, J;

Publication
EXPLAINABLE ARTIFICIAL INTELLIGENCE, XAI 2024, PT IV

Abstract
This study introduces a method to assess the quality of Explainable Artificial Intelligence (XAI) algorithms in dynamic data streams, concentrating on the fidelity and stability of feature-importance and rule-based explanations. We employ XAI metrics, such as fidelity and Lipschitz Stability, to compare explainers between each other and introduce the Comparative Expert Stability Index (CESI) for benchmarking explainers against domain knowledge. We adopted the aforementioned metrics to the streaming data scenario and tested them in an unsupervised classification scenario with simulated distribution shifts as different classes. The necessity for adaptable explainers in complex scenarios, like failure detection is underscored, stressing the importance of continued research into versatile explanation techniques to enhance XAI system robustness and interpretability.

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