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Publications

2024

Phasing segmented telescopes via deep learning methods: application to a deployable CubeSat

Authors
Dumont, M; Correia, CM; Sauvage, JF; Schwartz, N; Gray, M; Cardoso, J;

Publication
JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION

Abstract
Capturing high-resolution imagery of the Earth's surface often calls for a telescope of considerable size, even from low Earth orbits (LEOs). A large aperture often requires large and expensive platforms. For instance, achieving a resolution of 1 m at visible wavelengths from LEO typically requires an aperture diameter of at least 30 cm. Additionally, ensuring high revisit times often prompts the use of multiple satellites. In light of these challenges, a small, segmented, deployable CubeSat telescope was recently proposed creating the additional need of phasing the telescope's mirrors. Phasing methods on compact platforms are constrained by the limited volume and power available, excluding solutions that rely on dedicated hardware or demand substantial computational resources. Neural networks (NNs) are known for their computationally efficient inference and reduced onboard requirements. Therefore, we developed a NN-based method to measure co-phasing errors inherent to a deployable telescope. The proposed technique demonstrates its ability to detect phasing errors at the targeted performance level [typically a wavefront error (WFE) below 15 nm RMS for a visible imager operating at the diffraction limit] using a point source. The robustness of the NN method is verified in presence of high-order aberrations or noise and the results are compared against existing state-of-the-art techniques. The developed NN model ensures its feasibility and provides arealistic pathway towards achieving diffraction-limited images. (c) 2024 Optica Publishing Group

2024

Energy Efficiency Analysis of Differential and Omnidirectional Robotic Platforms: A Comparative Study

Authors
Chellal, AA; Braun, J; Bonzatto, L Jr; Faria, M; Kalbermatter, RB; Gonçalves, J; Costa, P; Lima, J;

Publication
SYNERGETIC COOPERATION BETWEEN ROBOTS AND HUMANS, VOL 1, CLAWAR 2023

Abstract
As robots have limited power sources. Energy optimization is essential to ensure an extension for their operating periods without needing to be recharged, thus maximizing their uptime and minimizing their running costs. This paper compares the energy consumption of different mobile robotic platforms, including differential, omnidirectional 3-wheel, omnidirectional 4-wheel, and Mecanum platforms. The comparison is based on the RobotAtFactory 4.0 competition that typically takes place during the Portuguese Robotics Open. The energy consumption from the batteries for each platform is recorded and compared. The experiments were conducted in a validated simulation environment with dynamic and friction models to ensure that the platforms operated at similar speeds and accelerations and through a 5200 mAh battery simulation. Overall, this study provides valuable information on the energy consumption of different mobile robotic platforms. Among other findings, differential robots are the most energy-efficient robots, while 4-wheel omnidirectional robots may offer a good balance between energy efficiency and maneuverability.

2024

EYE MOVEMENT PATTERNS IN WEB-BASED TASKS: THE INFLUENCE OF TARGET POSITION, INDIVIDUAL POSITIONING, AND TASK TYPE ON VISUAL INFORMATION PROCESSING (Update)

Authors
Vasconcelos-Raposo, J;

Publication
PSYCHTECH & HEALTH JOURNAL

Abstract
This paper is a conceptual and interpretative update of a previously published version. The main objective of this study was to understand how target position influences eye movements in navigational and informative tasks. The sample comprised 20 university students (13 females 7 males, aged 18-44). Participants completed a socio-demographic questionnaire and performed two tasks: navigational and informative. Eye movements were recorded during task performance. A 2x2 MANOVA was conducted to analyze linear combinations of dependent variables (blink duration, blink frequency, and fixation duration) across task types and target positions. Results revealed significant differences in eye movement patterns between tasks. The navigational task showed shorter average blink durations (204.236-1656.397 ms) and fewer blinks (1.987-9.786) compared to the informative task (553.598-1864.440 ms; 9.648-20.040 blinks, respectively). Strong interaction effects were observed between average fixation duration and individual position in both navigational (?p2 = .216) and informative (?p2 = .176) tasks. We conclude that target position in the navigational task significantly influences university students’ eye movements, while individual position affects eye movements in both navigational and informative tasks. These findings contribute to understanding how task demands modulate visual attention and potentially affect user interface design and educational technology.

2024

Adaptive Optics at W. M. Keck Observatory

Authors
Wizinowich, P; Bouchez, A; Marina, E; Cetre, S; China, J; Correia, C; van Dam, M; Delorme, JR; Gersa, L; Guthery, C; Karkar, S; Kwok, S; Lilley, S; Lyke, J; Richards, P; Service, M; Steiner, J; Surendran, A; Tsubota, K; Wetherell, E; Bottom, M; Dekany, R; Ghez, A; Hinz, P; Liue, M; Lu, J; Jensen-Clem, R; Millar-Blanchaer, M; Peretz, E; Sallum, S; Treu, T; Wright, S;

Publication
ADAPTIVE OPTICS SYSTEMS IX

Abstract
The first scientific observations with adaptive optics (AO) at W. M. Keck Observatory (WMKO) began in 1999. Through 2023, over 1200 refereed science papers have been published using data from the WMKO AO systems. The scientific competitiveness of AO at WMKO has been maintained through a continuous series of AO and instrument upgrades and additions. This tradition continues with AO being a centerpiece of WMKO's scientific strategic plan for 2035. We will provide an overview of the current and planned AO projects from the context of this strategic plan. The current projects include implementation of new real-time controllers, the KAPA laser tomography system and the HAKA high-order deformable mirror system, the development of multiple advanced wavefront sensing and control techniques, the ORCAS space-based guide star project, and three new AO science instruments. We will also summarize steps toward the future strategic directions which are centered on ground-layer, visible and high-contrast AO.

2024

Stability Analysis of DC Microgrids: Insights for Enhancing Renewable Energy Integration, Efficiency and Power Quality

Authors
Sousa, A; Grasel, B; Baptista, J;

Publication
APPLIED SCIENCES-BASEL

Abstract
In the current context of smart grids, microgrids have proven to be an effective solution to meet the energy needs of neighborhoods and collective buildings. This study investigates the voltage behavior and other critical parameters within a direct current (DC) microgrid to enhance system efficiency, stability, and reliability. The dynamic performance of a DC microgrid is analyzed under varying load and generation conditions, with particular emphasis on the voltage response and load-sharing mechanisms required to ensure stable operation. The findings indicate that specific control strategies, particularly droop methods, are effective in mitigating voltage fluctuations, enhancing power quality, and ensuring proper load distribution across multiple sources. This study also addresses significant challenges, including voltage regulation and fault resilience, to provide guidelines for designing robust and efficient DC microgrids. These insights are essential to inspire further advancements in control strategies and facilitate the practical deployment of DC microgrids as a sustainable solution for distributed energy systems, especially in scenarios prioritizing high DC load penetration and renewable energy integration.

2024

RIFF: Inducing Rules for Fraud Detection from Decision Trees

Authors
Martins, L; Bravo, J; Gomes, AS; Soares, C; Bizarro, P;

Publication
RULES AND REASONING, RULEML+RR 2024

Abstract
Financial fraud is the cause of multi-billion dollar losses annually. Traditionally, fraud detection systems rely on rules due to their transparency and interpretability, key features in domains where decisions need to be explained. However, rule systems require significant input from domain experts to create and tune, an issue that rule induction algorithms attempt to mitigate by inferring rules directly from data. We explore the application of these algorithms to fraud detection, where rule systems are constrained to have a low false positive rate (FPR) or alert rate, by proposing RIFF, a rule induction algorithm that distills a low FPR rule set directly from decision trees. Our experiments show that the induced rules are often able to maintain or improve performance of the original models for low FPR tasks, while substantially reducing their complexity and outperforming rules hand-tuned by experts.

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