arXiv subjects

Joana Teixeira

Publications and source records attributed to Joana Teixeira.

5 recordsLinked to original sources

arXiv2026

Photonic Extreme Learning Machines using Event-Based detection

Photonic extreme learning machines use random optical propagation, detection nonlinearity, and a trained linear readout for energy-efficient and scalable optical computing. However, conventional intensity readout with CCD or CMOS cameras constrain the dimensionality of the hidden representation space. Here, we experimentally replace intensity detection with event-based camera, whose thresholded log-intensity response provides alternative pixel-wise hidden representations: first-event time, binary activation, and event count. In nonlinear two spiral classification task we obtain accuracies of $93\pm 3\%$ with strong intrinsic generalization, and comparable ridge and pseudo-inverse performance indicating sample-limited effective dimensionality. Regression results reveal sensitivity to systematic optical-intensity drift, identifying stability requirements for future event-based PELMs. These results establish event-based detection as a route toward richer photonic hidden representations while clarifying current limitations.

physics.optics↗

arXiv2025

Multimodal Speckle-polarization Fiber-optic Sensing for Localized and High-bandwidth Vibration Monitoring

High-bandwidth and multi-point acoustic and vibration sensing is a critical asset for real-time condition monitoring, maintenance, and surveillance applications. In the case of large scales and harsh environments, optical fiber distributed sensing has emerged as a compelling alternative to electronic transducers, featuring lower installation and maintenance costs, along with compact footprints and enhanced robustness. Yet, current distributed fiber-optic sensing solutions are typically costly and face a resolution-bandwidth tradeoff. In this work, we present an alternative fiber-optic vibration sensing strategy that harnesses a multimodal architecture combining speckle and polarization interrogation. The experimental results demonstrate the concept by achieving speckle-based signal source localization with centimeter-range spatial resolution, while obtaining a high-fidelity waveform reconstruction over at least 100 Hz-40 kHz bandwidth via the polarimetric sensing part. Overall, the work establishes a general and promising blueprint to harness multimodality in fiber sensing and break single-modality constraints.

physics.optics↗

arXiv2025

Event-based Speckle Interrogation for High-Bandwidth Multi-point Optical Fiber Sensing

Speckle-based fiber optic sensors are well-known to offer high sensitivity but are strongly limited on the interrogation side by low camera frame rates and dynamic range. To address this limitation, we present a novel interrogation framework that explores event-based vision to achieve high throughput, high bandwidth, and low-latency speckle analysis of a multimode optical fiber sensor. In addition, leveraging a tensor-based decomposition of the raw event streams through multi-point calibration and machine-learning optimization, our approach also proves capable of isolating simultaneous deformations applied at distinct points. The experimental results validate the methodology by separating the signals of four piezoelectric actuators over a 400Hz-20kHz range with minimal crosstalk applied over varying distances from 3cm to 75cm. Finally, extending the impact of the work with an acoustic sensing proof-of-concept, we have coupled the fiber to two plastic enclosures and recovered separable audio signals between 400 and 1.8 kHz with minimal waveform distortion. Overall, these results establish event-driven speckle interrogation as a new versatile platform for real-time, multi-point acoustic sensing and pave for its application in complex and unstructured environments in future works.

physics.optics↗

arXiv2025

Where in the Milky Way Do Exoplanets Preferentially Form?

Exoplanets are detected around stars of different ages and birthplaces within the Galaxy. The aim of this work is to infer the Galactic birth radii ($r_\text{birth}$) of stars and, consequently, their planets, with the ultimate goal of studying the Galactic aspects of exoplanet formation. We used photometric, spectroscopic, and astrometric data to estimate the stellar ages of two samples of stars hosting planets and, for comparison, a sample of stars without detected planets. The $r_\text{birth}$ of exoplanets were inferred by projecting stars back to their birth positions based on their estimated age and metallicity [Fe/H]. We find that stars hosting planets have higher [Fe/H], are younger, and have smaller $r_\text{birth}$ compared to stars without detected planets. In particular, stars hosting high-mass planets show higher [Fe/H], are younger, and have smaller $r_\text{birth}$ than stars hosting low-mass planets. We show that the formation efficiency of planets, calculated as the relative frequency of planetary systems, decreases with the galactocentric distance, which relationship is stronger for high-mass planets than for low-mass planets. Additionally, we find that (i) the formation efficiency of high-mass planets increases with time and encompasses a larger galactocentric distance over time; (ii) the formation efficiency of low-mass planets shows a slight increase between the ages of 4 and 8 Gyr and also encompasses a larger galactocentric distance over time; and (iii) stars without detected planets appear to form at larger galactocentric distances over time. We conclude that the formation of exoplanets throughout the Galaxy follows the Galactic chemical evolution, for which our results are in agreement with the observed negative interstellar medium (ISM) metallicity gradient and its enrichment and flattening with time at any radius.

astro-ph.EP↗

arXiv2024

Generic gravito-magnetic clock effects

General relativity predicts that two counter-orbiting clocks around a spinning mass differ in the time required to complete the same orbit. The difference in these two values for the orbital period is generally referred to as the gravito-magnetic (GM) clock effect. It has been proposed to measure the GM clock effect using atomic clocks carried by satellites in prograde and retrograde orbits around the Earth. The precision and stability required for satellites to accurately perform this measurement remains a challenge for current instrumentation. One of the most accurate clocks in the Universe is a millisecond pulsar, which emits periodic radio pulses with high stability. Timing of the pulsed signals from millisecond pulsars has proven to be very successful in testing predictions of general relativity and the GM clock effect is potentially measurable in binary systems. In this work we derive the generic GM clock effect by considering a slowly-spinning binary system on an elliptical orbit, with both arbitrary mass ratio and arbitrary spin orientations. The spin-orbit interaction introduces a perturbation to the orbit, causing the orbital plane to precess and nutate. We identify several different contributions to the clock effects: the choice of spin supplementary condition and the observer-dependent definition of a full revolution and "nearly-identical" orbits. We discuss the impact of these subtle definitions on the formula for GM clock effects and show that most of the existing formulae in the literature can be recovered under appropriate assumptions.

gr-qc↗