Showing 1–50 of 252 results for author: Hernandez, S

Intrinsic limits of timekeeping precision in gene regulatory cascades

Authors: Juan Sebastian Hernandez, Cesar Nieto, Juan Manuel Pedraza, Abhyudai Singh

Abstract: Multiple cellular processes are triggered when the concentration of a regulatory protein reaches a critical threshold. Previous analyses have characterized timing statistics for single-gene systems. However, many biological timers are based on cascades of genes that activate each other sequentially. Here, we develop an analytical framework to describe the timing precision of such cascades using a… ▽ More Multiple cellular processes are triggered when the concentration of a regulatory protein reaches a critical threshold. Previous analyses have characterized timing statistics for single-gene systems. However, many biological timers are based on cascades of genes that activate each other sequentially. Here, we develop an analytical framework to describe the timing precision of such cascades using a burst-dilution hybrid stochastic model. We first revisit the single-gene case and recover the known result of an optimal activation threshold that minimizes first-passage-time (FPT) variability. Extending this concept to two-gene cascades, we identify three distinct optimization regimes determined by the ratio of intrinsic noise levels and the protein dilution rate, defining when coupling improves or worsens timing precision compared to a single-gene strategy. Generalizing to cascades of arbitrary gene length, we obtain a simple mathematical condition that determines when a new gene in the cascade can decrease the timing noise based on its intrinsic noise and protein dilution rate. In the specific case of a cascade of identical genes, our analytical results predict suppression of FPT noise with increasing cascade length and the existence of a mean time that decreases relative timing fluctuations. Together, these results define the intrinsic limits of timekeeping precision in gene regulatory cascades and provide a minimal analytical framework to explore timing control in biological systems. △ Less

Submitted 23 December, 2025; originally announced December 2025.

CLASSY XIV: The Nitrogen Exception -- Multi-Phase Enrichment and Feedback in High-$z$ Analogs

Authors: Bethan L. James, Valentina Abril-Melgarejo, Karla Z. Arellano-Córdova, Adarsh Ranjan, Kaelee S. Parker, Danielle A. Berg, Matilde Mingozzi, Alessandra Aloisi, John Chisholm, Timothy Heckman, Alaina Henry, Svea Hernandez, Kristen B. W. McQuinn, Xinfeng Xu, Chiaki Kobayashi, The CLASSY Collaboration

Abstract: We present a first-of-its-kind analysis of the metal content across two interstellar medium (ISM) phases in a sample of 31 local star-forming galaxies from the COS Legacy Archive Spectroscopic SurveY (CLASSY), selected as analogues of high-$z$ systems. Using co-spatial UV absorption and optical emission-line spectroscopy, we compare abundances of N, O, S, and Fe in the low-ionization (neutral) and… ▽ More We present a first-of-its-kind analysis of the metal content across two interstellar medium (ISM) phases in a sample of 31 local star-forming galaxies from the COS Legacy Archive Spectroscopic SurveY (CLASSY), selected as analogues of high-$z$ systems. Using co-spatial UV absorption and optical emission-line spectroscopy, we compare abundances of N, O, S, and Fe in the low-ionization (neutral) and high-ionization (ionized) gas, providing a multi-phase view of enrichment shortly after the current starburst and over longer timescales when ejecta from previous episodes have cooled and mixed. We find that O and S, produced predominantly in short-lived massive stars, are well mixed between the two phases, with scatter reflecting local inhomogeneities. Fe, predominantly produced by Type Ia supernovae on $\sim$1 Gyr timescales, is higher in the neutral gas, reflecting either delayed mixing of older Fe-enriched material or preferential depletion of Fe from the ionized phase through dust formation in core-collapse supernova ejecta. N exhibits the largest phase offset, with N/H$_{ion}$ systematically $\sim$0.7 dex higher than N/H$_{neu}$, and the magnitude of this offset correlates with stellar mass, metallicity, star-formation rate, and most strongly with the ISM outflow velocity. N/O ratios in the ionized phase rise rapidly within 3-6 Myr relative to the neutral gas, consistent with N enrichment dominated by Wolf-Rayet stars rather than intermediate-mass AGB stars on longer timescales. These results demonstrate that localized stellar feedback, outflows, and phase-dependent mixing collectively regulate the chemical evolution of star-forming galaxies, providing key insight into the extreme N/O abundances recently observed in galaxies at cosmic dawn. △ Less

Submitted 5 December, 2025; originally announced December 2025.

Comments: 32 pages, 15 figures, 10 tables, submitted to ApJ

CLASSY XIII. Cutting through the Clouds - Comparing Indirect Tracers of Ionizing Photon Escape

Authors: Kaelee S. Parker, Danielle A. Berg, John Chisholm, Simon Gazagnes, Sophia R. Flury, Cody Carr, Mason Huberty, Anne E. Jaskot, Matthew J. Hayes, Alberto Saldana-Lopez, Svea Hernandez, Themiya Nanayakkara, Bethan L. James, Karla Z. Arellano-Córdova, Allison Strom, Peter Senchyna, Matilde Mingozzi, Timothy Heckman, Xinfeng Xu, Alaina Henry, Ricardo O. Amorín, Valentin Mauerhofer, Crystal L. Martin, Dawn K. Erb, Evan D. Skillman , et al. (3 additional authors not shown)

Abstract: The Epoch of Reionization (EoR) provides critical insights into the role of early galaxies in shaping the ionization state of the universe. However, because of the opacity of the intergalactic medium, it is often not possible to make direct measurements of the ionizing photon escape fraction ($f_{\mathrm{esc}}^{\: \mathrm{LyC}}$) of high-redshift ($z \gtrsim 4$) galaxies. To explore the agreement… ▽ More The Epoch of Reionization (EoR) provides critical insights into the role of early galaxies in shaping the ionization state of the universe. However, because of the opacity of the intergalactic medium, it is often not possible to make direct measurements of the ionizing photon escape fraction ($f_{\mathrm{esc}}^{\: \mathrm{LyC}}$) of high-redshift ($z \gtrsim 4$) galaxies. To explore the agreement and systematics of common indirect approaches, we applied six empirically calibrated diagnostics to predict $f_{\mathrm{esc}}^{\: \mathrm{LyC}}$ for the 45 nearby star-forming galaxies from the COS Legacy Spectroscopic SurveY (CLASSY). These methods- based on ultraviolet (UV) absorption lines, the UV continuum slope, Ly$α$ kinematics, a multivariate model, radiation-hydrodynamic simulations, and nebular emission line ratios- enable us to explore systematic differences between predictions and assess how galactic properties influence inferred LyC escape. Despite significant variations in method predictions, there is broad consistency in the resulting weak and strong LyC leaker classifications, with approximately half exhibiting predicted escape fractions $>$1%. We find evidence for two different pathways of LyC escape in nearby star-forming galaxies: (1) an early escape model driven by very young stellar populations, and (2) a delayed escape model that is consistent with supernova-driven outflows and time-dependent ISM clearing. The early escape model is favored among galaxies with a single, intense burst of recent star formation. In contrast, the delayed escape model is common among galaxies with more extended starburst histories. To interpret ionizing photon escape during the EoR, it will be necessary to recognize and understand this diversity in LyC escape mechanisms. △ Less

Submitted 19 November, 2025; originally announced November 2025.

Comments: 26 pages with 12 figures and 4 tables. Accepted to ApJ

Predicting Barge Tow Size on Inland Waterways Using Vessel Trajectory Derived Features: Proof of Concept

Authors: Geoffery Agorku, Sarah Hernandez, Hayley Hames, Cade Wagner

Abstract: Accurate, real-time estimation of barge quantity on inland waterways remains a critical challenge due to the non-self-propelled nature of barges and the limitations of existing monitoring systems. This study introduces a novel method to use Automatic Identification System (AIS) vessel tracking data to predict the number of barges in tow using Machine Learning (ML). To train and test the model, bar… ▽ More Accurate, real-time estimation of barge quantity on inland waterways remains a critical challenge due to the non-self-propelled nature of barges and the limitations of existing monitoring systems. This study introduces a novel method to use Automatic Identification System (AIS) vessel tracking data to predict the number of barges in tow using Machine Learning (ML). To train and test the model, barge instances were manually annotated from satellite scenes across the Lower Mississippi River. Labeled images were matched to AIS vessel tracks using a spatiotemporal matching procedure. A comprehensive set of 30 AIS-derived features capturing vessel geometry, dynamic movement, and trajectory patterns were created and evaluated using Recursive Feature Elimination (RFE) to identify the most predictive variables. Six regression models, including ensemble, kernel-based, and generalized linear approaches, were trained and evaluated. The Poisson Regressor model yielded the best performance, achieving a Mean Absolute Error (MAE) of 1.92 barges using 12 of the 30 features. The feature importance analysis revealed that metrics capturing vessel maneuverability such as course entropy, speed variability and trip length were most predictive of barge count. The proposed approach provides a scalable, readily implementable method for enhancing Maritime Domain Awareness (MDA), with strong potential applications in lock scheduling, port management, and freight planning. Future work will expand the proof of concept presented here to explore model transferability to other inland rivers with differing operational and environmental conditions. △ Less

Submitted 27 October, 2025; originally announced October 2025.

The Long-Term Impact of Direct Capture Approaches to Carbon Dioxide Removal

Authors: Al Jay Lan J. Alamin, Melquezedec James T. Cruz, Bryan S. Hernandez, Eduardo R. Mendoza

Abstract: Understanding the similarities and differences of the long term impact of different carbon dioxide removal (CDR) techniques is essential in determining the most effective and sustainable strategies to mitigate climate change. In particular, direct ocean capture (DOC) has emerged as a promising approach. In contrast to direct air capture (DAC) which separates carbon dioxide from the atmosphere, DOC… ▽ More Understanding the similarities and differences of the long term impact of different carbon dioxide removal (CDR) techniques is essential in determining the most effective and sustainable strategies to mitigate climate change. In particular, direct ocean capture (DOC) has emerged as a promising approach. In contrast to direct air capture (DAC) which separates carbon dioxide from the atmosphere, DOC performs the separation directly from seawater before storing it in geological reservoirs. In this study, we construct and analyze a kinetic system for CDR via DOC using chemical reaction network theory. Our analysis reveals the necessary conditions for the existence of positive steady states and highlights the potential for multistationarity, where the carbon cycle may admit multiple positive steady states, emphasizing the critical importance of addressing tipping points, thresholds beyond which the system could undergo irreversible changes. Furthermore, we examine conditions under which certain carbon pools exhibit absolute concentration robustness, remaining resistant to change regardless of initial conditions. We also determine the conditions for the carbon reduction capability of the model with the DOC intervention. Importantly, a comparative analysis is then presented, where we compare the DOC model with the well-established DAC model by Fortun et al., and explore an integrated DOC-DAC approach for CDR. This comparison is important given that DAC is already being implemented in large-scale projects, while DOC remains in its early stages with limited trials and is geographically constrained to oceanic vicinity. Our comparative modeling framework provides valuable insights into the long-term impacts and complementary roles of DOC, DAC, and their integration into broader CDR strategies for climate mitigation. △ Less

Submitted 23 October, 2025; originally announced October 2025.

JWST/MIRI-MRS view of the metal-poor galaxy CGCG 007-025: the spatial location of PAHs and very highly ionized gas

Authors: Macarena G. del Valle-Espinosa, Matilde Mingozzi, Bethan James, Ruben Sanchez-Janssen, Juan Antonio Fernandez-Ontiveros, Ryan J. Rickards Vaught, Ricardo O. Amorin, Leslie Hunt, Alessandra Aloisi, Karla Z. Arellano-Cordova, Danielle A. Berg, John Chisholm, Matthew Hayes, Svea Hernandez, Alec Hirschauer, Logan Jones, Crystal L. Martin, Livia Vallini, Xinfeng Xu

Abstract: Polycyclic Aromatic Hydrocarbons (PAHs) are key diagnostics of the physical conditions in the interstellar medium and are widely used to trace star formation in the mid-infrared (mid-IR). The relative strengths of mid-IR PAH emission features (e.g., 6.2, 7.7, 11.3 um) are sensitive to both the size and ionization state of the molecules and can be strongly influenced by the local radiation field. H… ▽ More Polycyclic Aromatic Hydrocarbons (PAHs) are key diagnostics of the physical conditions in the interstellar medium and are widely used to trace star formation in the mid-infrared (mid-IR). The relative strengths of mid-IR PAH emission features (e.g., 6.2, 7.7, 11.3 um) are sensitive to both the size and ionization state of the molecules and can be strongly influenced by the local radiation field. However, at low metallicities ( Z < 0.2 Zsun), detecting PAHs remains notoriously difficult, likely reflecting a combination of suppressed formation and enhanced destruction mechanisms. We present new JWST/MIRI MRS observations of the metal-poor (Z = 0.1 Zsun) dwarf galaxy CGCG 007-025. We confirm the tentative PAH detection previously reported from Spitzer data and, for the first time, identify a compact (approx. 50 pc) PAH-emitting region nearly co-spatial with the newly detected [NeV](I.P. = 97 eV) emission and the galaxy's most metal-poor, strongly star-forming region. The 11.3 um PAH feature is clearly detected, while no emission is found from the other typically brighter features, suggesting a PAH population dominated by large, neutral molecules resilient to hard ionizing fields. When compared with models, mid-IR line ratios involving [NeIII], [OIV], and [NeV] can only be reproduced by a combination of star formation and AGN ionization, with the latter contributing 4--8%. The [OIV] and [NeV] luminosities exceed what massive stars or shocks can produce, highlighting a puzzling scenario in line with recent JWST observations of similar galaxies. This work provides a crucial reference for studying the physical conditions of the dust and star formation in low-metallicity starburst regions, environments typical of the early universe. △ Less

Submitted 13 October, 2025; originally announced October 2025.

Comments: Submitted to ApJL, 13 pages, 6 figures, 2 tables

Enhancing Maritime Domain Awareness on Inland Waterways: A YOLO-Based Fusion of Satellite and AIS for Vessel Characterization

Authors: Geoffery Agorku, Sarah Hernandez, Hayley Hames, Cade Wagner

Abstract: Maritime Domain Awareness (MDA) for inland waterways remains challenged by cooperative system vulnerabilities. This paper presents a novel framework that fuses high-resolution satellite imagery with vessel trajectory data from the Automatic Identification System (AIS). This work addresses the limitations of AIS-based monitoring by leveraging non-cooperative satellite imagery and implementing a fus… ▽ More Maritime Domain Awareness (MDA) for inland waterways remains challenged by cooperative system vulnerabilities. This paper presents a novel framework that fuses high-resolution satellite imagery with vessel trajectory data from the Automatic Identification System (AIS). This work addresses the limitations of AIS-based monitoring by leveraging non-cooperative satellite imagery and implementing a fusion approach that links visual detections with AIS data to identify dark vessels, validate cooperative traffic, and support advanced MDA. The You Only Look Once (YOLO) v11 object detection model is used to detect and characterize vessels and barges by vessel type, barge cover, operational status, barge count, and direction of travel. An annotated data set of 4,550 instances was developed from $5{,}973~\mathrm{mi}^2$ of Lower Mississippi River imagery. Evaluation on a held-out test set demonstrated vessel classification (tugboat, crane barge, bulk carrier, cargo ship, and hopper barge) with an F1 score of 95.8\%; barge cover (covered or uncovered) detection yielded an F1 score of 91.6\%; operational status (staged or in motion) classification reached an F1 score of 99.4\%. Directionality (upstream, downstream) yielded 93.8\% accuracy. The barge count estimation resulted in a mean absolute error (MAE) of 2.4 barges. Spatial transferability analysis across geographically disjoint river segments showed accuracy was maintained as high as 98\%. These results underscore the viability of integrating non-cooperative satellite sensing with AIS fusion. This approach enables near-real-time fleet inventories, supports anomaly detection, and generates high-quality data for inland waterway surveillance. Future work will expand annotated datasets, incorporate temporal tracking, and explore multi-modal deep learning to further enhance operational scalability. △ Less

Submitted 13 October, 2025; originally announced October 2025.

The height function of a sparse collection: a Bellman function approach

Authors: Shivam Aggarwal, Samuel Hernandez, Irina Holmes Fay, Jennifer Mackenzie

Abstract: Sparse operators have emerged as a powerful method to extract sharp constants in harmonic analysis inequalities, for example in the context of bounding singular integral operators. We investigate the level sets of height functions for sparse collections, or, in other words, weak-type (1,1) inequalities for sparse operators applied to constant functions. We use another notable method from dyadic ha… ▽ More Sparse operators have emerged as a powerful method to extract sharp constants in harmonic analysis inequalities, for example in the context of bounding singular integral operators. We investigate the level sets of height functions for sparse collections, or, in other words, weak-type (1,1) inequalities for sparse operators applied to constant functions. We use another notable method from dyadic harmonic analysis, also famous for its ability to produce sharp constants, the Bellman function method. Specifically, we find the exact Bellman function maximizing level sets of $\mathcal{A}_α1\!\!1$, where $\mathcal{A}_α$ is the (localized) sparse operator associated with a binary Carleson sequence. △ Less

Submitted 30 September, 2025; originally announced October 2025.

Combining Audio and Non-Audio Inputs in Evolved Neural Networks for Ovenbird

Authors: Sergio Poo Hernandez, Vadim Bulitko, Erin Bayne

Abstract: In the last several years the use of neural networks as tools to automate species classification from digital data has increased. This has been due in part to the high classification accuracy of image classification through Convolutional Neural Networks (CNN). In the case of audio data CNN based recognizers are used to automate the classification of species in audio recordings by using information… ▽ More In the last several years the use of neural networks as tools to automate species classification from digital data has increased. This has been due in part to the high classification accuracy of image classification through Convolutional Neural Networks (CNN). In the case of audio data CNN based recognizers are used to automate the classification of species in audio recordings by using information from sound visualization (i.e., spectrograms). It is common for these recognizers to use the spectrogram as their sole input. However, researchers have other non-audio data, such as habitat preferences of a species, phenology, and range information, available that could improve species classification. In this paper we present how a single-species recognizer neural network's accuracy can be improved by using non-audio data as inputs in addition to spectrogram information. We also analyze if the improvements are merely a result of having a neural network with a higher number of parameters instead of combining the two inputs. We find that networks that use the two different inputs have a higher classification accuracy than networks of similar size that use only one of the inputs. △ Less

Submitted 10 September, 2025; originally announced September 2025.

The Interstellar Medium in I Zw 18 seen with JWST/MIRI: II. Warm Molecular Hydrogen and Warm Dust

Authors: L. K. Hunt, B. T. Draine, M. G. Navarro, A. Aloisi, R. J. Rickards Vaught, A. Adamo, F. Annibali, D. Calzetti, S. Hernandez, B. L. James, M. Mingozzi, R. Schneider, M. Tosi, B. Brandl, M. G. del Valle-Espinosa, F. Donnan, A. S. Hirschauer, M. Meixner, D. Rigopoulou

Abstract: We present JWST/MIRI spectra from the Medium-Resolution Spectrometer of IZw18, a nearby dwarf galaxy with a metallicity of $\sim 3$% Solar. Here, we investigate warm molecular hydrogen, H2, observed in spectra extracted in $\sim 120$ pc apertures centered on eleven regions of interest. We detect 7 H2 rotational lines, some of which are among the weakest ever measured. The H2 population diagrams ar… ▽ More We present JWST/MIRI spectra from the Medium-Resolution Spectrometer of IZw18, a nearby dwarf galaxy with a metallicity of $\sim 3$% Solar. Here, we investigate warm molecular hydrogen, H2, observed in spectra extracted in $\sim 120$ pc apertures centered on eleven regions of interest. We detect 7 H2 rotational lines, some of which are among the weakest ever measured. The H2 population diagrams are fit with local-thermodynamic-equilibrium models and models of photodissociation regions. We also fit the ortho-/para-H2 ratios (OPRs); in three of the six regions for which it was possible to fit the OPR, we find values significantly greater than 3, the maximum value for local thermodynamic equilibrium. To our knowledge, although predicted theoretically, this is the first time that OPR significantly $> 3$ has been measured in interstellar gas. We find that OPR tends to increase with decreasing H2 column density, consistent with the expected effects of self-shielding in advancing photodissociation fronts. The population diagrams are consistent with H nucleon densities of $\sim 10^5$ cm$^{-3}$, and an interstellar radiation field scaling factor, G0, of $\sim 10^3$. This warm, dense H2 gas co-exists with the same highly ionized gas that emits [OIV] and [NeV]. Emission from T $\geq 50$K dust is detected, including an as-yet unidentified dust emission feature near 14 $μ$m; possible identification as Al$_2$O$_3$ is discussed. The continuum emission from several regions requires that a considerable fraction of the refractory elements be incorporated in dust. Despite stacking spectra in the SE where H2 is found, no significant emission from polycyclic aromatic hydrocarbons is detected. △ Less

Submitted 1 October, 2025; v1 submitted 2 September, 2025; originally announced September 2025.

Comments: 27 pages, 2 appendices, 14 figures, accepted for publication in ApJ. Updated to correct Figure 1

Combined dark matter search towards dwarf spheroidal galaxies with Fermi-LAT, HAWC, H.E.S.S., MAGIC, and VERITAS

Authors: Fermi-LAT Collaboration, :, S. Abdollahi, L. Baldini, R. Bellazzini, B. Berenji, E. Bissaldi, R. Bonino, P. Bruel, S. Buson, E. Charles, A. W. Chen, S. Ciprini, M. Crnogorcevic, A. Cuoco, F. D'Ammando, A. de Angelis, M. Di Mauro, N. Di Lalla, L. Di Venere, A. Domínguez, S. J. Fegan, A. Fiori, P. Fusco, V. Gammaldi , et al. (582 additional authors not shown)

Abstract: Dwarf spheroidal galaxies (dSphs) are excellent targets for indirect dark matter (DM) searches using gamma-ray telescopes because they are thought to have high DM content and a low astrophysical background. The sensitivity of these searches is improved by combining the observations of dSphs made by different gamma-ray telescopes. We present the results of a combined search by the most sensitive cu… ▽ More Dwarf spheroidal galaxies (dSphs) are excellent targets for indirect dark matter (DM) searches using gamma-ray telescopes because they are thought to have high DM content and a low astrophysical background. The sensitivity of these searches is improved by combining the observations of dSphs made by different gamma-ray telescopes. We present the results of a combined search by the most sensitive currently operating gamma-ray telescopes, namely: the satellite-borne Fermi-LAT telescope; the ground-based imaging atmospheric Cherenkov telescope arrays H.E.S.S., MAGIC, and VERITAS; and the HAWC water Cherenkov detector. Individual datasets were analyzed using a common statistical approach. Results were subsequently combined via a global joint likelihood analysis. We obtain constraints on the velocity-weighted cross section $\langle σ\mathit{v} \rangle$ for DM self-annihilation as a function of the DM particle mass. This five-instrument combination allows the derivation of up to 2-3 times more constraining upper limits on $\langle σ\mathit{v} \rangle$ than the individual results over a wide mass range spanning from 5 GeV to 100 TeV. Depending on the DM content modeling, the 95% confidence level observed limits reach $1.5\times$10$^{-24}$ cm$^3$s$^{-1}$ and $3.2\times$10$^{-25}$ cm$^3$s$^{-1}$, respectively, in the $τ^+τ^-$ annihilation channel for a DM mass of 2 TeV. △ Less

Submitted 27 August, 2025; originally announced August 2025.

Experimental End-to-End Optimization of Directly Modulated Laser-based IM/DD Transmission

Authors: Sergio Hernandez, Christophe Peucheret, Francesco Da Ros, Darko Zibar

Abstract: Directly modulated lasers (DMLs) are an attractive technology for short-reach intensity modulation and direct detection communication systems. However, their complex nonlinear dynamics make the modeling and optimization of DML-based systems challenging. In this paper, we study the end-to-end optimization of DML-based systems based on a data-driven surrogate model trained on experimental data. The… ▽ More Directly modulated lasers (DMLs) are an attractive technology for short-reach intensity modulation and direct detection communication systems. However, their complex nonlinear dynamics make the modeling and optimization of DML-based systems challenging. In this paper, we study the end-to-end optimization of DML-based systems based on a data-driven surrogate model trained on experimental data. The end-to-end optimization includes the pulse shaping and equalizer filters, the bias current and the modulation radio-frequency (RF) power applied to the laser. The performance of the end-to-end optimization scheme is tested on the experimental setup and compared to 4 different benchmark schemes based on linear and nonlinear receiver-side equalization. The results show that the proposed end-to-end scheme is able to deliver better performance throughout the studied symbol rates and transmission distances while employing lower modulation RF power, fewer filter taps and utilizing a smaller signal bandwidth. △ Less

Submitted 26 December, 2025; v1 submitted 27 August, 2025; originally announced August 2025.

Comments: 10 pages, 10 figures, published in journal of lightwave technology

Frequency Standard Contributions to Limitations on the Signal-to-Noise Ratio in Very Long Baseline Interferometric (VLBI) Observations

Authors: Eric Burt, Todd Ely, Geoff Bower, Joe Lazio, Marin Anderson, Sonia Hernandez

Abstract: Since its observation in 2019, the first image of a super-massive black hole using Very Long Baseline Interferometry (VLBI) with an Earth-scale baseline has generated much scientific and public interest, including the possible extension of the baseline into space to obtain higher image resolution. Operating one or more VLBI nodes in space will require the use of frequency standards that are space… ▽ More Since its observation in 2019, the first image of a super-massive black hole using Very Long Baseline Interferometry (VLBI) with an Earth-scale baseline has generated much scientific and public interest, including the possible extension of the baseline into space to obtain higher image resolution. Operating one or more VLBI nodes in space will require the use of frequency standards that are space qualified, greatly reducing the number of options available. The coherence function C(T) is the metric usually used to determine the viability of a frequency standard. Here we show that C(T) is a useful but not sufficient metric for gauging frequency standard performance in VLBI and instead derive an expression for the clock-limited VLBI visibility S/N. We evaluate this expression for real frequency standards and find only the Ultra-Stable Oscillator (USO) and hydrogen maser to be viable for upcoming high-frequency VLBI with the USO only useful for very limited integration times (30s at 90 GHz, 10s at 230 GHz, 5s at 345 GHz, and not viable at 630 GHz). The maser extends these, but may have prohivitive size for a space mission. We also evaluate emerging frequency standard technologies and find the Optical Local Oscillator portion of optical clocks to be very promising (conservatively >100s at 90 GHz, 60s at 230 GHz, 40s at 345 GHz, and 22s at 630 GHz) when accounting for both performance and potential operation in space. △ Less

Submitted 26 August, 2025; originally announced August 2025.

C60 fullerene as an on-demand single photon source at room temperature

Authors: Raul Lahoz Sanz, Lidia Lozano Martín, Adrià Brú i Cortés, Sergi Hernández, Martí Duocastella, José M. Gómez-Cama, Bruno Juliá-Díaz

Abstract: Single photon sources are fundamental for applications in quantum computing, secure communication, and sensing, as they enable the generation of individual photons and ensure strict control over photon number statistics. However, current single photon sources can be limited by a lack of robustness, difficulty of integration into existing optical or electronic devices, and high cost. In this study,… ▽ More Single photon sources are fundamental for applications in quantum computing, secure communication, and sensing, as they enable the generation of individual photons and ensure strict control over photon number statistics. However, current single photon sources can be limited by a lack of robustness, difficulty of integration into existing optical or electronic devices, and high cost. In this study, we present the use of off-the-shelf \ch{C60} fullerene molecules embedded in polystyrene as room-temperature reliable single-photon emitters. As our results demonstrate, these molecules exhibit on-demand single-photon emission, with short fluorescence lifetimes and, consequently, high emission rates. The wide availability and ease of preparation and manipulation of fullerenes as single photon sources can pave the way for the development of practical, economic and scalable quantum photonic technologies. △ Less

Submitted 25 August, 2025; originally announced August 2025.

Comments: Authors' version of the article submitted to Nano Letters

The Compilation and Validation of the Spectroscopic Redshift Catalogs for the DESI-COSMOS and DESI-XMMLSS Fields

Authors: J. Ratajczak, K. S. Dawson, N. Weaverdyck, J. Aguilar, S. Ahlen, E. Armengaud, S. Bailey, D. Bianchi, D. Blanco, A. Brodzeller, D. Brooks, F. J. Castander, T. Claybaugh, A. Cuceu, A. de la Macorra, Arjun Dey, Biprateep Dey, P. Doel, A. Font-Ribera, J. E. Forero-Romero, E. Gaztañaga, S. Gontcho A Gontcho, G. Gutierrez, J. Guy, T. Hagen , et al. (52 additional authors not shown)

Abstract: Over several dedicated programs that include targets beyond the main cosmological samples, the Dark Energy Spectroscopic Instrument (DESI) collected spectra for 304,970 unique objects in two fields centered on the COSMOS and XMM-LSS fields. In this work, we develop spectroscopic redshift robustness criteria for those spectra, validate these criteria using visual inspection, and provide two custom… ▽ More Over several dedicated programs that include targets beyond the main cosmological samples, the Dark Energy Spectroscopic Instrument (DESI) collected spectra for 304,970 unique objects in two fields centered on the COSMOS and XMM-LSS fields. In this work, we develop spectroscopic redshift robustness criteria for those spectra, validate these criteria using visual inspection, and provide two custom Value-Added Catalogs with our redshift characterizations. With these criteria, we reliably classify 212,935 galaxies below z < 1.6, 9,713 quasars and 35,222 stars. As a critical element in characterizing the selection function, we provide the description of 70 different algorithms that were used to select these targets from imaging data. To facilitate joint imaging/spectroscopic analyses, we provide row-matched photometry from the Dark Energy Camera, Hyper-Suprime Cam, and public COSMOS2020 photometric catalogs. Finally, we demonstrate example applications of these large catalogs to photometric redshift estimation, cluster finding, and completeness studies. △ Less

Submitted 27 August, 2025; v1 submitted 12 August, 2025; originally announced August 2025.

The Interstellar Medium in IZw18 seen with JWST/MIRI: I. Highly Ionized Gas

Authors: L. K. Hunt, A. Aloisi, M. G. Navarro, R. J. Rickards Vaught, B. T. Draine, A. Adamo, F. Annibali, D. Calzetti, S. Hernandez, B. L. James, M. Mingozzi, R. Schneider, M. Tosi, B. Brandl, M. G. del Valle-Espinosa, F. Donnan, A. S. Hirschauer, M. Meixner, D. Rigopoulou, C. T. Richardson, J. M. Levanti, A. R. Basu-Zych

Abstract: We present JWST/MIRI spectra from the Medium-Resolution Spectrometer of IZw18, a nearby dwarf galaxy with a metallicity of $\sim$3% Solar. Its proximity enables a detailed study of highly ionized gas that can be interpreted in the context of newly discovered high-redshift dwarf galaxies. We derive aperture spectra centered on eleven regions of interest; the spectra show very low extinction, A_V… ▽ More We present JWST/MIRI spectra from the Medium-Resolution Spectrometer of IZw18, a nearby dwarf galaxy with a metallicity of $\sim$3% Solar. Its proximity enables a detailed study of highly ionized gas that can be interpreted in the context of newly discovered high-redshift dwarf galaxies. We derive aperture spectra centered on eleven regions of interest; the spectra show very low extinction, A_V $\lesssim 0.1$, consistent with optical determinations. The gas is highly ionized; we have detected 10 fine-structure lines, including [OIV] 25.9 micron with an ionization potential (IP) of $\sim$ 55 eV, and [NeV] 14.3 micron with an IP of $\sim$ 97 eV. The ionization state of IZw18 falls at the extreme upper end of all of the line ratios we analyzed, but not coincident with galaxies containing an accreting massive black hole (active galactic nucleus). Comparison of the line ratios with state-of-the-art photoionization and shock models suggests that the high ionization state in IZw18 is not due to shocks. Rather it can be attributed to metal-poor stellar populations with a self-consistent contribution of X-ray binaries or ultra-luminous X-ray sources. It could also be partially due to a small number of hot low-metallicity Wolf-Rayet stars ionizing the gas; a small fraction (a few percent) of the ionization could come from an intermediate-mass black hole. Our spectroscopy also revealed four 14 micron continuum sources, $\gtrsim 30-100$ pc in diameter, three of which were not previously identified. Their properties are consistent with HII regions ionized by young star clusters. △ Less

Submitted 12 August, 2025; originally announced August 2025.

Comments: 28 pages, 12 figures, 2 appendices; accepted for publication in ApJ

XUE 10. The CO2-rich terrestrial planet-forming region of an externally irradiated Herbig disk

Authors: Jenny Frediani, Arjan Bik, María Claudia Ramírez-Tannus, Rens Waters, Konstantin V. Getman, Eric D. Feigelson, Bayron Portilla-Revelo, Benoît Tabone, Thomas J. Haworth, Andrew Winter, Thomas Henning, Giulia Perotti, Alexis Brandeker, Germán Chaparro, Pablo Cuartas-Restrepo, Sebastián Hernández, Michael A. Kuhn, Thomas Preibisch, Veronica Roccatagliata, Sierk E. van Terwisga, Peter Zeidler

Abstract: We investigate the James Webb Space Telescope (JWST) MIRI MRS gas molecular content of an externally irradiated Herbig disk, the F-type XUE 10 source, in the context of the eXtreme UV Environments (XUE) program. XUE 10 belongs to the massive star cluster NGC 6357 (1.69 kpc), where it is exposed to an external far-ultraviolet (FUV) radiation $\approx$ 10$^3$ times stronger than in the Solar neighbo… ▽ More We investigate the James Webb Space Telescope (JWST) MIRI MRS gas molecular content of an externally irradiated Herbig disk, the F-type XUE 10 source, in the context of the eXtreme UV Environments (XUE) program. XUE 10 belongs to the massive star cluster NGC 6357 (1.69 kpc), where it is exposed to an external far-ultraviolet (FUV) radiation $\approx$ 10$^3$ times stronger than in the Solar neighborhood. We modeled the molecular features in the mid-infrared spectrum with Local Thermodynamic Equilibrium (LTE) 0D slab models. We derived basic parameters of the stellar host from a VLT FORS2 optical spectrum using PHOENIX stellar templates. We detect bright CO2 gas with the first simultaneous detection (> 5$σ$) of four isotopologues (12CO2, 13CO2, 16O12C18O, 16O12C17O) in a protoplanetary disk. We also detect faint CO emission (2$σ$) and the HI Pf$α$ line (8$σ$). We also place strict upper limits on the water content, finding a total column density $\lesssim$ 10$^{18}$ cm$^{-2}$. The CO2 species trace low gas temperatures (300-370 K) with a range of column densities of 7.4 $\times$ 10$^{17}$ cm$^{-2}$ (16O12C17O)-1.3 $\times$ 10$^{20}$ cm$^{-2}$ (12CO2) in an equivalent emitting radius of 1.15 au. The emission of 13CO2 is likely affected by line optical depth effects. 16O12C18O and 16O12C17O abundances may be isotopically anomalous compared to the 16O/18O and 16O/17O ratios measured in the interstellar medium and the Solar System. We propose that the mid-infrared spectrum of XUE 10 is explained by H2O removal either via advection or strong photo-dissociation by stellar UV irradiation, and enhanced local CO2 gas-phase production. Outer disk truncation supports the observed CO2-H2O dichotomy. A CO2 vapor enrichment in 18O and 17O can be explained by means of external UV irradiation and early on (10$^{4-5}$ yr) delivery of isotopically anomalous water ice to the inner disk. △ Less

Submitted 24 July, 2025; v1 submitted 18 July, 2025; originally announced July 2025.

Comments: 20 pages, 13 figures, 4 tables

The Interstellar Medium in I Zw 18 seen with JWST/MIRI: III. Spatially Resolved Three Ionization State Oxygen Abundance

Authors: Ryan J. Rickards Vaught, Leslie K. Hunt, Alessandra Aloisi, Maria G. Navarro-Ovando, Matilde Mingozzi, Bethan James, Macarena G. del Valle-Espinosa, Karin M. Sandstrom, Angela Adamo, Francesca Annibali, Daniela Calzetti, B. T. Draine, Svea Hernandez, Alec S. Hirschauer, Margaret Meixner, Dimitra Rigopoulou, Monica Tosi

Abstract: We present observations of the nearby extremely metal-poor galaxy I Zw 18 using the Keck Cosmic Web Imager (KCWI) and the JWST Mid-InfraRed Instrument (MIRI) Integral Field Spectrographs (IFS). From optical and mid-IR oxygen emission lines, we measured direct-method abundances for three ionic states of oxygen, including O$^{3+}$/H$^+$. In contrast to previous studies of I Zw 18, the high spatial r… ▽ More We present observations of the nearby extremely metal-poor galaxy I Zw 18 using the Keck Cosmic Web Imager (KCWI) and the JWST Mid-InfraRed Instrument (MIRI) Integral Field Spectrographs (IFS). From optical and mid-IR oxygen emission lines, we measured direct-method abundances for three ionic states of oxygen, including O$^{3+}$/H$^+$. In contrast to previous studies of I Zw 18, the high spatial resolution afforded by KCWI and MIRI/MRS revealed chemical inhomogeneities on 60 pc scales in the form of metal-poor pockets and metal-enriched gas. These are located outside I Zw 18's star-forming complexes having possibly been dispersed beyond these regions via stellar feedback effects. We found that metallicities derived using a single low-ionization density tracer, and T$_{\rm e}$([O II]) derived from a temperature relationship commonly used in high-$z$ galaxy studies, exhibited the largest scatter and underestimated the metallicity compared to those derived using multi-ion densities and estimated T$_{\rm e}$([N II]). Finally, we compared O$^{3+}$/H$^+$ abundances from a theoretical ionization correction factor (ICF) against observed values and found that the oxygen ICF underestimates the O$^{3+}$/H$^+$ abundance by a factor of 2, indicating that either additional ionizing sources are needed or standard stellar population models are unable to produce the requisite ionizing flux. △ Less

Submitted 16 July, 2025; originally announced July 2025.

Comments: Accepted to ApJ

CLASSY XII: Nitrogen Enrichment Shaped by Gas Density and Feedback

Authors: Karla Z. Arellano-Córdova, Danielle A. Berg, Matilde Mingozzi, Bethan L. James, Fiorenzo Vincenzo, Noah S. J. Rogers, Evan D. Skillman, Ricardo O. Amorín, Fergus Cullen, Sophia R. Flury, Valentina Abril-Melgarejo, John Chisholm, Timothy Heckman, Matthew J. Hayes, Svea Hernandez, Nimisha Kumari, Chiaki Kobayashi, Claus Leitherer, Crystal L. Martin, Zorayda Martinez, Themiya Nanayakkara, Kaelee S. Parker, Peter Senchyna, Claudia Scarlata, Mabel G. Stephenson , et al. (3 additional authors not shown)

Abstract: We investigate the chemical evolution of N/O using a sample of 45 local star-forming galaxies (SFGs) from the CLASSY survey. This sample spans a wide range of galaxy properties, with robust determinations of nitrogen and oxygen abundances via the direct-$T_{\rm e}$ method. We explore how N/O relates to density structure, stellar mass, star formation rate (SFR), stellar age, compactness, and gas ki… ▽ More We investigate the chemical evolution of N/O using a sample of 45 local star-forming galaxies (SFGs) from the CLASSY survey. This sample spans a wide range of galaxy properties, with robust determinations of nitrogen and oxygen abundances via the direct-$T_{\rm e}$ method. We explore how N/O relates to density structure, stellar mass, star formation rate (SFR), stellar age, compactness, and gas kinematics. In addition, we compare our results with those of galaxies at $z =2-10$ where N/O ratios were derived from optical or UV nitrogen lines, aiming to identify chemical enrichment pathways across cosmic time. Our analysis shows that the N/O-O/H relation in CLASSY galaxies aligns with the trends seen in local galaxies and extragalactic HII regions, and that galaxies at $z = 2-6$ exhibit similar N/O values, indicating no significant redshift evolution in N/O for a fixed metallicity. We identify a significant correlation between electron density $n_{\rm e}$([S II]) and N/O, suggesting that density structure contributes to the scatter in the N/O-O/H relation. The CLASSY galaxies with high SFRs or compact star formation show elevated N/O, though no strong correlation with stellar mass is found. We also find that high-velocity outflows (v$_{out}$ > 350 km/s) and low mass-loading factors are linked to elevated N/O, indicating that feedback plays a significant role. These results highlight the importance of density, star formation, and feedback from young stellar populations in shaping N/O enrichment and provide key insights for interpreting high-$z$ galaxies observed with JWST. △ Less

Submitted 5 October, 2025; v1 submitted 15 July, 2025; originally announced July 2025.

Comments: MNRAS accepted. Minor changes. Figures 3 and 4 updated

Gemini 2.5: Pushing the Frontier with Advanced Reasoning, Multimodality, Long Context, and Next Generation Agentic Capabilities

Authors: Gheorghe Comanici, Eric Bieber, Mike Schaekermann, Ice Pasupat, Noveen Sachdeva, Inderjit Dhillon, Marcel Blistein, Ori Ram, Dan Zhang, Evan Rosen, Luke Marris, Sam Petulla, Colin Gaffney, Asaf Aharoni, Nathan Lintz, Tiago Cardal Pais, Henrik Jacobsson, Idan Szpektor, Nan-Jiang Jiang, Krishna Haridasan, Ahmed Omran, Nikunj Saunshi, Dara Bahri, Gaurav Mishra, Eric Chu , et al. (3410 additional authors not shown)

Abstract: In this report, we introduce the Gemini 2.X model family: Gemini 2.5 Pro and Gemini 2.5 Flash, as well as our earlier Gemini 2.0 Flash and Flash-Lite models. Gemini 2.5 Pro is our most capable model yet, achieving SoTA performance on frontier coding and reasoning benchmarks. In addition to its incredible coding and reasoning skills, Gemini 2.5 Pro is a thinking model that excels at multimodal unde… ▽ More In this report, we introduce the Gemini 2.X model family: Gemini 2.5 Pro and Gemini 2.5 Flash, as well as our earlier Gemini 2.0 Flash and Flash-Lite models. Gemini 2.5 Pro is our most capable model yet, achieving SoTA performance on frontier coding and reasoning benchmarks. In addition to its incredible coding and reasoning skills, Gemini 2.5 Pro is a thinking model that excels at multimodal understanding and it is now able to process up to 3 hours of video content. Its unique combination of long context, multimodal and reasoning capabilities can be combined to unlock new agentic workflows. Gemini 2.5 Flash provides excellent reasoning abilities at a fraction of the compute and latency requirements and Gemini 2.0 Flash and Flash-Lite provide high performance at low latency and cost. Taken together, the Gemini 2.X model generation spans the full Pareto frontier of model capability vs cost, allowing users to explore the boundaries of what is possible with complex agentic problem solving. △ Less

Submitted 19 December, 2025; v1 submitted 7 July, 2025; originally announced July 2025.

Comments: 72 pages, 17 figures

CLUES III: Do User Choices Impact The Results of SED Fitting? Tests of 'Off-The-Shelf' Stellar Population and Dust Extinction Models in the CLUES Sample

Authors: Andrew Mizener, Daniela Calzetti, Angela Adamo, Aida Wofford, Matthew J. Hayes, John Chisholm, Michele Fumagalli, Svea Hernandez, Matteo Maria Messa, Linda J. Smith, Arjan Bik, Kathryn Grasha, Mattia Sirressi

Abstract: The simple stellar population models produced by stellar population and spectral synthesis (SPS) codes are used as spectral templates in a variety of astrophysical contexts. In this paper, we test the predictions of four commonly used stellar population synthesis codes (YGGDRASIL, BPASS, FSPS, and a modified form of GALAXEV which we call GALAXEVneb) by using them as spectral templates for photomet… ▽ More The simple stellar population models produced by stellar population and spectral synthesis (SPS) codes are used as spectral templates in a variety of astrophysical contexts. In this paper, we test the predictions of four commonly used stellar population synthesis codes (YGGDRASIL, BPASS, FSPS, and a modified form of GALAXEV which we call GALAXEVneb) by using them as spectral templates for photometric SED fitting with a sample of 18 young stellar clusters. All clusters have existing HST COS FUV spectroscopy that provide constraints on their ages as well as broadband photometry from HST ACS and WFC3. We use model spectra that account for both nebular and stellar emission, and additionally test four extinction curves at different values of $R_V$. We find that for individual clusters, choice of extinction curve and SPS model can introduce significant scatter into the results of SED fitting. Model choice can introduce scatter of 34.8 Myr in age, a factor of 9.5 in mass, and 0.40mag in extinction. Extinction curve choice can introduce scatter of up to a factor of 32.3 Myr in age, a factor of 10.4 in mass, and 0.41mag in extinction. We caution that because of this scatter, one-to-one comparisons between the properties of individual objects derived using different SED fitting setups may not be meaningful. However, our results also suggest that SPS model and extinction curve choice do not introduce major systematic differences into SED fitting results when the entire cluster population is considered. The distribution of cluster properties for a large enough sample is relatively robust to user choice of SPS code and extinction curve. △ Less

Submitted 2 June, 2025; originally announced June 2025.

Comments: 41 pages, 17 figures

Creation of a degenerate Bose-Bose mixture of erbium and lithium atoms

Authors: Jasmine Kalia, Jared Rivera, Rubaiya R Emran, William J Solorio Hernandez, Kiryang Kwon, Richard J Fletcher

Abstract: We report the realization of a degenerate mixture of $^{166}$Er and $^{7}$Li atoms in their energetically lowest spin states. The two species are sequentially laser-cooled and loaded into an optical dipole trap, then transported to a glass cell and simultaneously evaporated to degeneracy. Er serves as the coolant for Li, and we observe efficient sympathetic cooling facilitated by a large interspec… ▽ More We report the realization of a degenerate mixture of $^{166}$Er and $^{7}$Li atoms in their energetically lowest spin states. The two species are sequentially laser-cooled and loaded into an optical dipole trap, then transported to a glass cell and simultaneously evaporated to degeneracy. Er serves as the coolant for Li, and we observe efficient sympathetic cooling facilitated by a large interspecies elastic scattering cross section. Three-body losses are found to be small, making this platform promising for the study of interacting mixtures with large mass imbalance. △ Less

Submitted 27 October, 2025; v1 submitted 30 May, 2025; originally announced June 2025.

Comments: 8 pages, 3 figures, 3 appendices

PDPO: Parametric Density Path Optimization

Authors: Sebastian Gutierrez Hernandez, Peng Chen, Haomin Zhou

Abstract: We introduce Parametric Density Path Optimization (PDPO), a novel method for computing action-minimizing paths between probability densities. The core idea is to represent the target probability path as the pushforward of a reference density through a parametric map, transforming the original infinite-dimensional optimization over densities to a finite-dimensional one over the parameters of the ma… ▽ More We introduce Parametric Density Path Optimization (PDPO), a novel method for computing action-minimizing paths between probability densities. The core idea is to represent the target probability path as the pushforward of a reference density through a parametric map, transforming the original infinite-dimensional optimization over densities to a finite-dimensional one over the parameters of the map. We derive a static formulation of the dynamic problem of action minimization and propose cubic spline interpolation of the path in parameter space to solve the static problem. Theoretically, we establish an error bound of the action under proper assumptions on the regularity of the parameter path. Empirically, we find that using 3-5 control points of the spline interpolation suffices to accurately resolve both multimodal and high-dimensional problems. We demonstrate that PDPO can flexibly accommodate a wide range of potential terms, including those modeling obstacles, mean-field interactions, stochastic control, and higher-order dynamics. Our method outperforms existing state-of-the-art approaches in benchmark tasks, demonstrating superior computational efficiency and solution quality. The source code will be publically available after the revision process. △ Less

Submitted 5 December, 2025; v1 submitted 23 May, 2025; originally announced May 2025.

Comments: 28 pages, 16 figures

Journal ref: NeurIPS 2025

XUE. JWST spectroscopy of externally irradiated disks around young intermediate-mass stars

Authors: María Claudia Ramírez-Tannus, Arjan Bik, Konstantin V. Getman, Rens Waters, Bayron Portilla-Revelo, Christiane Göppl, Andrew Winter, Jenny Frediani, Germán Chaparro, Eric D. Feigelson, Thomas J. Haworth, Thomas Henning, Sebastián Hernández, M. Alejandra Lemus-Nemocón, Michael Kuhn, Thomas Preibisch, Veronica Roccatagliata, Elena Sabbi, Roy van Boekel, Peter Zeidler

Abstract: Most young stars and therefore planetary systems form in high-mass star forming regions and are exposed to ultraviolet radiation, affecting the protoplanetary disk. These regions are located at large distances and only now with JWST become accessible to study the inner disks surrounding young stars. We present the eXtreme UV Environments (XUE) program, which provides the first detailed characteriz… ▽ More Most young stars and therefore planetary systems form in high-mass star forming regions and are exposed to ultraviolet radiation, affecting the protoplanetary disk. These regions are located at large distances and only now with JWST become accessible to study the inner disks surrounding young stars. We present the eXtreme UV Environments (XUE) program, which provides the first detailed characterization of the physical and chemical properties of the inner disks around young intermediate-mass stars exposed to external irradiation from nearby massive stars. We present high signal to noise MIRI-MRS spectroscopy of 12 disks located in three sub-clusters of the high-mass star-forming region NGC 6357. Based on their mid-infrared spectral energy distribution, we classify the XUE sources into Group I and II based on the Meeus scheme. We analyze their molecular emission features, and compare their spectral indices and 10 $μ$m silicate emission profiles to those of nearby Herbig and intermediate T Tauri disks. Despite being more massive, the XUE stars host disks with molecular richness comparable to isolated T Tauri systems. The 10 $μ$m silicate features show lower F$_{11.3}$/F$_{9.8}$ ratios at a given F$_{\mathrm{peak}}$, but current uncertainties prevent conclusions about their inner disk properties. Most disks display water emission from the inner disk, suggesting that even in these extreme environments rocky planets can form in the presence of water. The absence of strong line fluxes and other irradiation signatures suggests that the XUE disks have been truncated by external UV photons. However, this truncation does not appear to significantly impact the chemical richness of their inner regions. These findings indicate that even in extreme environments, IMTT disks can retain the ingredients necessary for rocky planet formation. △ Less

Submitted 28 July, 2025; v1 submitted 9 May, 2025; originally announced May 2025.

Comments: 14 pages, 8 appendix, 16 figures, 2 tables. Accepted version before language editing by A&A

Journal ref: A&A 701, A139 (2025)

A characterization of closed subfunctors through $3\times 3$-lemma property in extriangulated categories

Authors: Juan C. Cala, Shaira R. Hernández

Abstract: Given an extriangulated category $(\mathcal{C},\mathbb{E},\mathfrak{s})$, we introduce the $3 \times 3$-lemma property for subfunctors of $\mathbb{E}$ and prove that an additive subfunctor $\mathbb{F}$ of $\mathbb{E}$ is closed if, and only if, it satisfies this condition. This characterization extends a well known result by A. Buan (for abelian categories) to extriangulated categories. As an appl… ▽ More Given an extriangulated category $(\mathcal{C},\mathbb{E},\mathfrak{s})$, we introduce the $3 \times 3$-lemma property for subfunctors of $\mathbb{E}$ and prove that an additive subfunctor $\mathbb{F}$ of $\mathbb{E}$ is closed if, and only if, it satisfies this condition. This characterization extends a well known result by A. Buan (for abelian categories) to extriangulated categories. As an application of this result, we get a new equivalent condition to describe saturated proper classes $ξ$ in $\mathcal{C}$. △ Less

Submitted 22 April, 2025; originally announced April 2025.

Comments: 10 pages

MSC Class: 18G80; 18G10; 18G25

CMS RPC Non-Physics Event Data Automation Ideology

Authors: A. Dimitrov, M. Tytgat, K. Mota Amarilo, A. Samalan, K. Skovpen, G. A. Alves, E. Alves Coelho, F. Marujo da Silva, M. Barroso Ferreira Filho, E. M. Da Costa, D. De Jesus Damiao, S. Fonseca De Souza, R. Gomes De Souza, L. Mundim, H. Nogima, J. P. Pinheiro, A. Santoro, M. Thiel, A. Aleksandrov, R. Hadjiiska, P. Iaydjiev, M. Shopova, G. Sultanov, L. Litov, B. Pavlov , et al. (79 additional authors not shown)

Abstract: This paper presents a streamlined framework for real-time processing and analysis of condition data from the CMS experiment Resistive Plate Chambers (RPC). Leveraging data streaming, it uncovers correlations between RPC performance metrics, like currents and rates, and LHC luminosity or environmental conditions. The Java-based framework automates data handling and predictive modeling, integrating… ▽ More This paper presents a streamlined framework for real-time processing and analysis of condition data from the CMS experiment Resistive Plate Chambers (RPC). Leveraging data streaming, it uncovers correlations between RPC performance metrics, like currents and rates, and LHC luminosity or environmental conditions. The Java-based framework automates data handling and predictive modeling, integrating extensive datasets into synchronized, query-optimized tables. By segmenting LHC operations and analyzing larger virtual detector objects, the automation enhances monitoring precision, accelerates visualization, and provides predictive insights, revolutionizing RPC performance evaluation and future behavior modeling. △ Less

Submitted 11 April, 2025; originally announced April 2025.

Comments: CMS RPC Condition Data Automation, Java framework, 12 pages, 23 figures, CMS Condition database

The UV Legacy Library of Young Stars as Essential Standards (ULLYSES) Large Director's Discretionary Program with Hubble. I. Goals, Design, and Initial Results

Authors: Julia Roman-Duval, William J. Fischer, Alexander W. Fullerton, Jo Taylor, Rachel Plesha, Charles Proffitt, TalaWanda Monroe, Travis C. Fischer, Alessandra Aloisi, Jean-Claude Bouret, Christopher Britt, Nuria Calvet, Joleen K. Carlberg, Paul A. Crowther, Gisella De Rosa, William V. Dixon, Catherine C. Espaillat, Christopher J. Evans, Andrew J. Fox, Kevin France, Miriam Garcia, Sott W. Fleming, Elaine M. Frazer, Ana I. Gómez De Castro, Gregory J. Herczeg , et al. (22 additional authors not shown)

Abstract: Specifically selected to leverage the unique ultraviolet capabilities of the Hubble Space Telescope, the Hubble Ultraviolet Legacy Library of Young Stars as Essential Standards (ULLYSES) is a Director's Discretionary program of approximately 1000 orbits - the largest ever executed - that produced a UV spectroscopic library of O and B stars in nearby low metallicity galaxies and accreting low mass… ▽ More Specifically selected to leverage the unique ultraviolet capabilities of the Hubble Space Telescope, the Hubble Ultraviolet Legacy Library of Young Stars as Essential Standards (ULLYSES) is a Director's Discretionary program of approximately 1000 orbits - the largest ever executed - that produced a UV spectroscopic library of O and B stars in nearby low metallicity galaxies and accreting low mass stars in the Milky Way. Observations from ULLYSES combined with archival spectra uniformly sample the fundamental astrophysical parameter space for each mass regime, including spectral type, luminosity class, and metallicity for massive stars, and the mass, age, and disk accretion rate for low-mass stars. The ULLYSES spectral library of massive stars will be critical to characterize how massive stars evolve at different metallicities; to advance our understanding of the production of ionizing photons, and thus of galaxy evolution and the re-ionization of the Universe; and to provide the templates necessary for the synthesis of integrated stellar populations. The massive star spectra are also transforming our understanding of the interstellar and circumgalactic media of low metallicity galaxies. On the low-mass end, UV spectra of T Tauri stars contain a plethora of diagnostics of accretion, winds, and the warm disk surface. These diagnostics are crucial for evaluating disk evolution and provide important input to assess atmospheric escape of planets and to interpret powerful probes of disk chemistry, as observed with ALMA and JWST. In this paper we motivate the design of the program, describe the observing strategy and target selection, and present initial results. △ Less

Submitted 7 April, 2025; originally announced April 2025.

Comments: 58 pages, 20 figures

Phase Diagrams Construction Using Mean-Field Renormalization and Neural Network Fitting

Authors: Esteban Bedoya Rodriguez, Leon Escobar Diaz, Sebastian Trujillo Hernandez

Abstract: Employing the mean-field renormalization group (MFRG) method, we analyzed the $Fe_p Mn_{0.6-p}Al_{0.4}$ and $Fe_{p}Al_{1-p}$ alloys, incorporating second-neighbor interactions in the latter for the first time within this framework. Our analysis utilized neural network fitting, yielding promising results in both the phase diagram adjustments and the estimation of bond energies. Employing the mean-field renormalization group (MFRG) method, we analyzed the $Fe_p Mn_{0.6-p}Al_{0.4}$ and $Fe_{p}Al_{1-p}$ alloys, incorporating second-neighbor interactions in the latter for the first time within this framework. Our analysis utilized neural network fitting, yielding promising results in both the phase diagram adjustments and the estimation of bond energies. △ Less

Submitted 27 February, 2025; originally announced March 2025.

Extension of continuous functions on product spaces, Bohr Compactification and Almost Periodic Functions

Authors: Salvador Hernández

Abstract: The Bohr compactification is a well known construction for (topological) groups and semigroups. Recently, this notion has been investigated for arbitrary structures in \cite{har_kun:bohr_discrete} where the Bohr compactification is defined, using a set-theoretical approach, as the maximal compactification which is compatible with the structure involved. Here, we give a characterization of the cont… ▽ More The Bohr compactification is a well known construction for (topological) groups and semigroups. Recently, this notion has been investigated for arbitrary structures in \cite{har_kun:bohr_discrete} where the Bohr compactification is defined, using a set-theoretical approach, as the maximal compactification which is compatible with the structure involved. Here, we give a characterization of the continuous functions defined on a product space that can be extended continuously to certain compactifications of the product space. As a consequence, the Bohr compactification of an arbitrary topological structure is obtained as the Gelfand space of the commutative Banach algebra of all almost periodic functions. Previously, almost periodic functions $f$ are defined in terms of translates of $f$ with no reference to any compactification of the underlying structure. An application is given to the representation of isometries defined between spaces of almost periodic functions. △ Less

Submitted 11 March, 2025; originally announced March 2025.

MSC Class: 46E25; 05C38; 15A15; 05A15; 15A18 05A15; 15A18

Journal ref: Topology Proceedings (2004)

JWST/MIRI detection of [Ne V] and [Ne VI] in M83: Evidence for the long sought-after AGN?

Authors: Svea Hernandez, Linda J. Smith, Logan H. Jones, Aditya Togi, Marcio B. Melendez, Valentina Abril-Melgarejo, Angela Adamo, Almudena Alonso Herrero, Tanio Diaz-Santos, Travis C. Fischer, Santiago Garcia-Burillo, Alec S. Hirschauer, Leslie K. Hunt, Bethan James, Vianney Lebouteiller, Knox S. Long, Matilde Mingozzi, Lise Ramambason, Cristina Ramos Almeida

Abstract: We report the first detections of [Ne V] 14.3 μm and [Ne VI] 7.7 μm at high confidence (S/N>=6) in the nuclear region of the nearby spiral galaxy M83. Emission line maps of these high ionization lines show several compact structures. Specifically, the [Ne VI] emission is located at 140 pc from the optical nucleus and appears as a point source of size ~<18 pc (FWHM =<0.8"). We investigate the possi… ▽ More We report the first detections of [Ne V] 14.3 μm and [Ne VI] 7.7 μm at high confidence (S/N>=6) in the nuclear region of the nearby spiral galaxy M83. Emission line maps of these high ionization lines show several compact structures. Specifically, the [Ne VI] emission is located at 140 pc from the optical nucleus and appears as a point source of size ~<18 pc (FWHM =<0.8"). We investigate the possible source of this extreme emission through comparison with photoionization models and ancillary data. We find that photoionization models of fast radiative shocks are able to reproduce the observed high excitation emission line fluxes only for the lowest preshock density available in the library, n =0.01 cm^-3. Additionally, tailored active galactic nuclei (AGN) photoionization models assuming a two-zone structure are compatible with the observed high ionization fluxes. Our simple AGN model shows that the emission at the location of the [Ne VI] source can be the result of a cloud being ionized by the radiation cone of an AGN. We stress, however, that to definitively confirm an AGN as the main source of the observed emission, more complex modeling accounting for different geometries is required. Previously known as a purely starburst system, these new findings of the nuclear region of M83 will require a reassessment of its nature and of objects similar to it, particularly now that we have access to the unparalleled infrared sensitivity and spatial resolution of the James Webb Space Telescope. △ Less

Submitted 24 February, 2025; originally announced February 2025.

Comments: 12 pages, 8 figures, 1 table, Accepted for publication in ApJ

Group homomorphisms induced by isometries

Authors: Salvador Hernández

Abstract: Let $G$ and $H$ be locally compact groups and consider their associate spaces of almost periodic functions $AP(G)$ and $AP(H)$. We investigate the continuous group homomorphisms induced by isometries of $AP(G)$ into $AP(H)$. Among others, the following results are proved: {\bf Theorem} Let $G$ and $H$ be $σ$-compact maximally almost periodic locally compact groups. Suppose that $T$ is a non-vani… ▽ More Let $G$ and $H$ be locally compact groups and consider their associate spaces of almost periodic functions $AP(G)$ and $AP(H)$. We investigate the continuous group homomorphisms induced by isometries of $AP(G)$ into $AP(H)$. Among others, the following results are proved: {\bf Theorem} Let $G$ and $H$ be $σ$-compact maximally almost periodic locally compact groups. Suppose that $T$ is a non-vanishing linear isometry of $AP(G)$ into $AP(H)$ that respects finite dimensional unitary representations. Then there is a closed subgroup $H_0\subseteq H$, a continuous group homomorphism $t$ of $H_0$ onto $G$ and an character $γ\in \widehat{H}$ such that $(Tf)(h)=γ(h)~f(t(h))$ for all $h\in H_0$ and for all $f\in C(G)$. {\bf Theorem} Let $G$ and $H$ be $LC$ Abelian groups and $H$ is connected. Suppose that $T$ is a non-vanishing linear isometry of $AP(G)$ into $AP(H)$ that preserves trigonometric polynomials. Then there is a closed subgroup $H_0\subseteq H$, a continuous group homomorphism $t$ of $H_0$ onto $G$, an element $h_0\in H_0$, a character $α\in \widehat{H}$ and an unimodular complex number $a$ such that $(Tf)(h)=a\cdot α(h)~\cdot f(t(h-h_0))\text{ for all }h\in H_0\text{ and for all }f\in C(G)\text{.}$ △ Less

Submitted 23 February, 2025; originally announced February 2025.

MSC Class: 22D35; 43A60; 46E15; 54C40; 43A40

Journal ref: Topology Proceedings (2003)

Exploring the mysterious high-ionization source powering [Ne V] in high-z analog SBS0335-052 E with JWST/MIRI

Authors: Matilde Mingozzi, Macarena Garcia Del Valle-Espinosa, Bethan L. James, Ryan J. Rickards Vaught, Matthew Hayes, Ricardo O. Amorín, Claus Leitherer, Alessandra Aloisi, Leslie Hunt, David Law, Chris Richardson, Aidan Pidgeon, Karla Z. Arellano-Córdova, Danielle A. Berg, John Chisholm, Svea Hernandez, Logan Jones, Nimisha Kumari, Crystal L. Martin, Swara Ravindranath, Livia Vallini, Xinfeng Xu

Abstract: Nearby blue compact dwarf galaxies (BCDs) share similar properties with objects from the Epoch of Reionization revealed by JWST, in terms of low stellar mass, low metallicity and high specific star-formation rate. Thus, they represent ideal local laboratories for detailed multi-wavelength studies to understand their properties and the mechanisms shaping them. We report the first JWST MIRI/MRS obse… ▽ More Nearby blue compact dwarf galaxies (BCDs) share similar properties with objects from the Epoch of Reionization revealed by JWST, in terms of low stellar mass, low metallicity and high specific star-formation rate. Thus, they represent ideal local laboratories for detailed multi-wavelength studies to understand their properties and the mechanisms shaping them. We report the first JWST MIRI/MRS observations of the BCD SBS 0335-052 E, analyzing MIR emission lines tracing different levels of ionization (e.g., [NeII], [SIV], [NeIII], [OIV], [NeV]) of the ionized gas. SBS 0335-052 E MIR emission is characterized by a bright point source, located in one of the youngest and most embedded stellar clusters ($t\sim3$ Myr, $A_V\sim15$), and underlying extended high-ionization emission (i.e., [OIV], [NeV]) from the surroundings of the older and less dusty stellar clusters ($t< 20 $ Myr, $A_V\sim8$). From the comparison with state-of-the-art models, we can exclude shocks, X-ray binaries, and old stellar populations as the main sources of the high ionization. Interestingly, a 4-16% contribution of a $\sim10^5$ M$_\odot$ intermediate massive black hole (IMBH) is needed to justify the strong [NeV]/[NeII] and would be consistent with optical/UV line ratios from previous studies. However, even IMBH models cannot explain the strongest [OIV]/[NeIII]. Also, star-forming models (regardless of including X-ray binaries) struggle to reproduce even the lower ionization line ratios (e.g., [SIV]/[NeII]) typically observed in BCDs. Overall, while current models suggest the need to account for an accreting IMBH in this high-$z$ analog, limitations still exist in predicting high-ionization emission lines (I.P. $>54$ eV) when modeling these low-metallicity environments, thus other sources of ionization cannot be fully ruled out. △ Less

Submitted 29 May, 2025; v1 submitted 11 February, 2025; originally announced February 2025.

Comments: Accepted for publication in ApJ

Dark photon constraints using the UHE gamma-ray emission from galactic sources. A Phenomenological Study

Authors: Arlette Melo, Sergio Hernández, Rubén Alfaro

Abstract: Context: Dark photons (Dph) appear in theories beyond the Standard Model of particles (SM). Under certain conditions, it is possible to have a mixing between SM photons and Dphs that should be observed as anomalies in the spectrum of astrophysical sources. Aim: To either find evidence of, or set constraints on the existence of Dphs with masses in the range of $μ\text{eV}$ using observations of two… ▽ More Context: Dark photons (Dph) appear in theories beyond the Standard Model of particles (SM). Under certain conditions, it is possible to have a mixing between SM photons and Dphs that should be observed as anomalies in the spectrum of astrophysical sources. Aim: To either find evidence of, or set constraints on the existence of Dphs with masses in the range of $μ\text{eV}$ using observations of two galactic sources observed at TeV energies. Methods: Using the flux of the Crab Nebula and MGRO J1908+06 at TeV energies reported by HAWC and LHAASO observatories, and assuming a model where Dphs can mix with SM photons in the vacuum; we compute the Test Statistic (TS) to search for evidence of Dphs in the form of variations/attenuation in the observed spectrum. Results: We do not find statistically significant evidence of the existence of $μ\text{eV}$ Dphs. Then, we compute the 68\% C.L. and 95\% C.L. exclusion regions for Dphs with masses in the range from $10^{-8}$ to $10^{-5}~\text{eV}$ and mixing angles with values between 0.01 and 1.0. △ Less

Submitted 30 January, 2025; originally announced January 2025.

Comments: 8 pages, 2 tables, 6 figures, article

Explaining GitHub Actions Failures with Large Language Models: Challenges, Insights, and Limitations

Authors: Pablo Valenzuela-Toledo, Chuyue Wu, Sandro Hernandez, Alexander Boll, Roman Machacek, Sebastiano Panichella, Timo Kehrer

Abstract: GitHub Actions (GA) has become the de facto tool that developers use to automate software workflows, seamlessly building, testing, and deploying code. Yet when GA fails, it disrupts development, causing delays and driving up costs. Diagnosing failures becomes especially challenging because error logs are often long, complex and unstructured. Given these difficulties, this study explores the potent… ▽ More GitHub Actions (GA) has become the de facto tool that developers use to automate software workflows, seamlessly building, testing, and deploying code. Yet when GA fails, it disrupts development, causing delays and driving up costs. Diagnosing failures becomes especially challenging because error logs are often long, complex and unstructured. Given these difficulties, this study explores the potential of large language models (LLMs) to generate correct, clear, concise, and actionable contextual descriptions (or summaries) for GA failures, focusing on developers' perceptions of their feasibility and usefulness. Our results show that over 80\% of developers rated LLM explanations positively in terms of correctness for simpler/small logs. Overall, our findings suggest that LLMs can feasibly assist developers in understanding common GA errors, thus, potentially reducing manual analysis. However, we also found that improved reasoning abilities are needed to support more complex CI/CD scenarios. For instance, less experienced developers tend to be more positive on the described context, while seasoned developers prefer concise summaries. Overall, our work offers key insights for researchers enhancing LLM reasoning, particularly in adapting explanations to user expertise. △ Less

Submitted 27 January, 2025; originally announced January 2025.

Comments: Accepted at ICPC-2025

Shedding Light on Naked Singularities

Authors: Franco Fiorini, Santiago Hernandez, Juan Manuel Paez

Abstract: Electromagnetic waves propagating in the background provided by a spacetime hosting a strong curvature, naked singularity, are fully studied. The analysis is performed not only in the realm of geometrical optics -- which, not surprisingly, proves to be inadequate in the strong field regime characterizing the vicinity of the singularity -- but also in the physical one in which the field amplitudes… ▽ More Electromagnetic waves propagating in the background provided by a spacetime hosting a strong curvature, naked singularity, are fully studied. The analysis is performed not only in the realm of geometrical optics -- which, not surprisingly, proves to be inadequate in the strong field regime characterizing the vicinity of the singularity -- but also in the physical one in which the field amplitudes must necessarily be incorporated into the description. In addition to the expected divergent outcome with regard to the field amplitudes and power flux as the waves approach the singularity, we found a number of regular (bounded) solutions which seem to coexist with the unbridled effects of the spacetime curvature. In some of them, the singularity operates as a perfect mirror reflecting the surrounding fields. Strikingly, other solutions exhibit a perfectly well behaved, bounded power flux as they propagate towards the singularity, suggesting thus the possibility of having electromagnetic energy transference through it. △ Less

Submitted 19 April, 2025; v1 submitted 9 January, 2025; originally announced January 2025.

Comments: 7 pages, 2 figures. Accepted for publication in Phys. Lett. B

Journal ref: Phys. Lett. B865 (2025) 139478

Predicting Barge Presence and Quantity on Inland Waterways using Vessel Tracking Data: A Machine Learning Approach

Authors: Geoffery Agorku, Sarah Hernandez, Maria Falquez, Subhadipto Poddar, Shihao Pang

Abstract: This study presents a machine learning approach to predict the number of barges transported by vessels on inland waterways using tracking data from the Automatic Identification System (AIS). While AIS tracks the location of tug and tow vessels, it does not monitor the presence or number of barges transported by those vessels. Understanding the number and types of barges conveyed along river segmen… ▽ More This study presents a machine learning approach to predict the number of barges transported by vessels on inland waterways using tracking data from the Automatic Identification System (AIS). While AIS tracks the location of tug and tow vessels, it does not monitor the presence or number of barges transported by those vessels. Understanding the number and types of barges conveyed along river segments, between ports, and at ports is crucial for estimating the quantities of freight transported on the nation's waterways. This insight is also valuable for waterway management and infrastructure operations impacting areas such as targeted dredging operations, and data-driven resource allocation. Labeled sample data was generated using observations from traffic cameras located along key river segments and matched to AIS data records. A sample of 164 vessels representing up to 42 barge convoys per vessel was used for model development. The methodology involved first predicting barge presence and then predicting barge quantity. Features derived from the AIS data included speed measures, vessel characteristics, turning measures, and interaction terms. For predicting barge presence, the AdaBoost model achieved an F1 score of 0.932. For predicting barge quantity, the Random Forest combined with an AdaBoost ensemble model achieved an F1 score of 0.886. Bayesian optimization was used for hyperparameter tuning. By advancing predictive modeling for inland waterways, this study offers valuable insights for transportation planners and organizations, which require detailed knowledge of traffic volumes, including the flow of commodities, their destinations, and the tonnage moving in and out of ports. △ Less

Submitted 11 July, 2025; v1 submitted 31 December, 2024; originally announced January 2025.

OpenAI o1 System Card

Authors: OpenAI, :, Aaron Jaech, Adam Kalai, Adam Lerer, Adam Richardson, Ahmed El-Kishky, Aiden Low, Alec Helyar, Aleksander Madry, Alex Beutel, Alex Carney, Alex Iftimie, Alex Karpenko, Alex Tachard Passos, Alexander Neitz, Alexander Prokofiev, Alexander Wei, Allison Tam, Ally Bennett, Ananya Kumar, Andre Saraiva, Andrea Vallone, Andrew Duberstein, Andrew Kondrich , et al. (238 additional authors not shown)

Abstract: The o1 model series is trained with large-scale reinforcement learning to reason using chain of thought. These advanced reasoning capabilities provide new avenues for improving the safety and robustness of our models. In particular, our models can reason about our safety policies in context when responding to potentially unsafe prompts, through deliberative alignment. This leads to state-of-the-ar… ▽ More The o1 model series is trained with large-scale reinforcement learning to reason using chain of thought. These advanced reasoning capabilities provide new avenues for improving the safety and robustness of our models. In particular, our models can reason about our safety policies in context when responding to potentially unsafe prompts, through deliberative alignment. This leads to state-of-the-art performance on certain benchmarks for risks such as generating illicit advice, choosing stereotyped responses, and succumbing to known jailbreaks. Training models to incorporate a chain of thought before answering has the potential to unlock substantial benefits, while also increasing potential risks that stem from heightened intelligence. Our results underscore the need for building robust alignment methods, extensively stress-testing their efficacy, and maintaining meticulous risk management protocols. This report outlines the safety work carried out for the OpenAI o1 and OpenAI o1-mini models, including safety evaluations, external red teaming, and Preparedness Framework evaluations. △ Less

Submitted 21 December, 2024; originally announced December 2024.

Finest decomposition coarsening of reaction networks of biochemical systems

Authors: Bryan S. Hernandez, Juan Paolo C. Santos, Patrick Vincent N. Lubenia, Eduardo R. Mendoza

Abstract: Biochemical reaction networks are typically modeled by $\dfrac{dx}{dt}=N\cdot K(x)=Y\cdot I_a\cdot K(x)$, with $x$ and $K(x)$ as the concentration and rate vectors, respectively, and $N$, $Y$, and $I_a$ as the stoichiometric, molecularity, and incidence matrices, respectively. Steady states, which describe their long-term behaviors, are determined by solving $N\cdot K(x)=0$, while complex balanced… ▽ More Biochemical reaction networks are typically modeled by $\dfrac{dx}{dt}=N\cdot K(x)=Y\cdot I_a\cdot K(x)$, with $x$ and $K(x)$ as the concentration and rate vectors, respectively, and $N$, $Y$, and $I_a$ as the stoichiometric, molecularity, and incidence matrices, respectively. Steady states, which describe their long-term behaviors, are determined by solving $N\cdot K(x)=0$, while complex balanced steady states are found by solving $I_a \cdot K(x)=0$. To investigate these complex networks, decomposition techniques are important, in particular, for computing steady states. Previously, we identified a widespread property across many networks: the existence of independent and incidence-independent decompositions, characterized by the ability to directly sum the stoichiometric and incidence matrices of the subnetworks, respectively, to match those of the entire network. Here, we discover the ubiquitous property that we call the Finest Decomposition Coarsening (FDC), where the finest independent decomposition (FID) is a coarsening of the finest incidence-independent decomposition (FIID). To support the analysis of this property, we introduce a MATLAB package designed to compute both these decompositions. We then characterize the FDC property and its relationship to structural factors such as the invertibility of the molecularity matrix. We also introduce and characterize the Finest Decompositions Equality (FDE) property, where FIID equals FID. Notably, we show that all deficiency zero networks exhibit the FDE property. Furthermore, we establish important relationships of the FID and FIID with decomposition of the network into its connected components. Our results highlight the prevalence of the coarsening property in reaction networks and deepens the understanding of the algebraic structure and dynamics of biochemical networks. △ Less

Submitted 4 December, 2024; originally announced December 2024.

Soliton generation through temporal reflection in media with a frequency-dependent nonlinearity

Authors: Lucas N. Gutierrez, Pablo I. Fierens, Diego F. Grosz, Santiago M. Hernandez

Abstract: We demonstrate that the temporal reflection of a weak dispersive pulse on a soliton in media with a frequency-dependent nonlinearity leads to the generation of new solitons, whose number can be selected by tuning parameters of the dispersive pulse. By carefully analyzing the different processes involved, we show that a virtuous interplay between Raman scattering and a zero-nonlinearity wavelength… ▽ More We demonstrate that the temporal reflection of a weak dispersive pulse on a soliton in media with a frequency-dependent nonlinearity leads to the generation of new solitons, whose number can be selected by tuning parameters of the dispersive pulse. By carefully analyzing the different processes involved, we show that a virtuous interplay between Raman scattering and a zero-nonlinearity wavelength is a key enabler for soliton generation to occur, limiting the initial soliton redshift and allowing for an efficient energy transfer between the dispersive pulse and its reflection. Finally, we believe results presented in this work may contribute guidelines for the generation of short and intense pulses for various photonic applications. △ Less

Submitted 4 December, 2024; originally announced December 2024.

Comments: 4 pages (+ 1 full references page), letter

Experimental Demonstration of End-to-End Optimization for Directly Modulated Laser-based IM/DD Systems

Authors: Sergio Hernandez, Christophe Peucheret, Francesco Da Ros, Darko Zibar

Abstract: We experimentally demonstrate the joint optimization of transmitter and receiver parameters in directly modulated laser systems, showing superior performance compared to nonlinear receiver-only equalization while using fewer memory taps, less bandwidth, and lower radiofrequency power. We experimentally demonstrate the joint optimization of transmitter and receiver parameters in directly modulated laser systems, showing superior performance compared to nonlinear receiver-only equalization while using fewer memory taps, less bandwidth, and lower radiofrequency power. △ Less

Submitted 23 October, 2024; originally announced October 2024.

Comments: submitted to the Optical Fiber Conference (OFC)

A JWST/MIRI View of the ISM in M83: I. Resolved Molecular Hydrogen Properties, Star Formation, and Feedback

Authors: Logan H. Jones, Svea Hernandez, Linda J. Smith, Aditya Togi, Tanio Diaz-Santos, Alessandra Aloisi, William Blair, Alec S. Hirschauer, Leslie K. Hunt, Bethan L. James, Nimisha Kumari, Vianney Lebouteiller, Matilde Mingozzi, Lise Ramambason

Abstract: We present a spatially-resolved (~3 pc pix$^{-1}$) analysis of the distribution, kinematics, and excitation of warm H2 gas in the nuclear starburst region of M83. Our JWST/MIRI IFU spectroscopy reveals a clumpy reservoir of warm H2 (> 200 K) with a mass of ~2.3 x 10$^{5}$ Msun in the area covered by all four MRS channels. We additionally use the [Ne II] 12.8 $μ$m and [Ne III] 15.5 $μ$m lines as tr… ▽ More We present a spatially-resolved (~3 pc pix$^{-1}$) analysis of the distribution, kinematics, and excitation of warm H2 gas in the nuclear starburst region of M83. Our JWST/MIRI IFU spectroscopy reveals a clumpy reservoir of warm H2 (> 200 K) with a mass of ~2.3 x 10$^{5}$ Msun in the area covered by all four MRS channels. We additionally use the [Ne II] 12.8 $μ$m and [Ne III] 15.5 $μ$m lines as tracers of the star formation rate, ionizing radiation hardness, and kinematics of the ionized ISM, finding tantalizing connections to the H2 properties and to the ages of the underlying stellar populations. Finally, qualitative comparisons to the trove of public, high-spatial-resolution multiwavelength data available on M83 shows that our MRS spectroscopy potentially traces all stages of the process of creating massive star clusters, from the embedded proto-cluster phase through the dispersion of ISM from stellar feedback. △ Less

Submitted 11 October, 2024; originally announced October 2024.

Comments: 21 pages, 11+1 figures; submitted to ApJ

Segment Anything Model for Grain Characterization in Hard Drive Design

Authors: Kai Nichols, Matthew Hauwiller, Nicholas Propes, Shaowei Wu, Stephanie Hernandez, Mike Kautzky

Abstract: Development of new materials in hard drive designs requires characterization of nanoscale materials through grain segmentation. The high-throughput quickly changing research environment makes zero-shot generalization an incredibly desirable feature. For this reason, we explore the application of Meta's Segment Anything Model (SAM) to this problem. We first analyze the out-of-the-box use of SAM. Th… ▽ More Development of new materials in hard drive designs requires characterization of nanoscale materials through grain segmentation. The high-throughput quickly changing research environment makes zero-shot generalization an incredibly desirable feature. For this reason, we explore the application of Meta's Segment Anything Model (SAM) to this problem. We first analyze the out-of-the-box use of SAM. Then we discuss opportunities and strategies for improvement under the assumption of minimal labeled data availability. Out-of-the-box SAM shows promising accuracy at property distribution extraction. We are able to identify four potential areas for improvement and show preliminary gains in two of the four areas. △ Less

Submitted 22 August, 2024; originally announced August 2024.

Comments: This paper has been accepted by the International Workshop on Computer Vision for Materials Science in conjunction with the IEEE/CVF CVPR 2024

Stochastic Variance-Reduced Iterative Hard Thresholding in Graph Sparsity Optimization

Authors: Derek Fox, Samuel Hernandez, Qianqian Tong

Abstract: Stochastic optimization algorithms are widely used for large-scale data analysis due to their low per-iteration costs, but they often suffer from slow asymptotic convergence caused by inherent variance. Variance-reduced techniques have been therefore used to address this issue in structured sparse models utilizing sparsity-inducing norms or $\ell_0$-norms. However, these techniques are not directl… ▽ More Stochastic optimization algorithms are widely used for large-scale data analysis due to their low per-iteration costs, but they often suffer from slow asymptotic convergence caused by inherent variance. Variance-reduced techniques have been therefore used to address this issue in structured sparse models utilizing sparsity-inducing norms or $\ell_0$-norms. However, these techniques are not directly applicable to complex (non-convex) graph sparsity models, which are essential in applications like disease outbreak monitoring and social network analysis. In this paper, we introduce two stochastic variance-reduced gradient-based methods to solve graph sparsity optimization: GraphSVRG-IHT and GraphSCSG-IHT. We provide a general framework for theoretical analysis, demonstrating that our methods enjoy a linear convergence speed. Extensive experiments validate △ Less

Submitted 23 July, 2024; originally announced July 2024.

Mapping Multi-Phase Metals in Star-forming Galaxies: a spatially resolved UV + Optical Study of NGC 5253

Authors: Valentina Abril-Melgarejo, Bethan L. James, Alessandra Aloisi, Matilde Mingozzi, Vianney Lebouteiller, Svea Hernandez, Nimisha Kumari

Abstract: We present a pioneering spatially-resolved, multi-phase gas abundance study on the blue compact dwarf galaxy NGC~5253, targeting 10 star-forming (SF) clusters inside six FUV HST/COS pointings with co-spatial optical VLT/MUSE observations throughout the galaxy. The SF regions span a wide range of ages (1--15 Myr) and are distributed at different radii (50 -- 230 pc). We performed robust absorption-… ▽ More We present a pioneering spatially-resolved, multi-phase gas abundance study on the blue compact dwarf galaxy NGC~5253, targeting 10 star-forming (SF) clusters inside six FUV HST/COS pointings with co-spatial optical VLT/MUSE observations throughout the galaxy. The SF regions span a wide range of ages (1--15 Myr) and are distributed at different radii (50 -- 230 pc). We performed robust absorption-line profile fitting on the COS spectra, covering 1065--1430 Å in the FUV, allowing an accurate computation of neutral-gas abundances for 13 different ions sampling 8 elements. These values were then compared with the ionized-gas abundances, measured using the direct method on MUSE integrated spectra inside analog COS apertures. Our multi-phase, spatially resolved comparisons find abundances which are lower in the neutral gas than the ionized gas by 0.22 dex, 0.80 dex and 0.58 dex for log(O/H), log(N/H) and log(N/O), respectively. We modeled the chemical abundance distributions and evaluated correlations as a function of radius and age. It was found that while N, O and N/O abundances decrease as a function of age in the ionized gas, they increase with age in the neutral gas. No strong correlations for N, O or N/O were observed as a function of radius. The N/O and N/H offsets between the phases were found to decrease with age, providing evidence that chemical enrichment happens differentially, first in the ionized-gas phase around 2--5 Myrs (due to N-rich Wolf-Rayet stars) and then mixing out into the cold neutral gas on longer timescales of 10--15 Myr. △ Less

Submitted 24 June, 2024; originally announced June 2024.

Comments: 40 pages, 14 Figures. Revised version submitted to ApJ

Pushing the limits of the Cosmic Origin Spectrograph (COS) with an optimized background correction

Authors: Svea Hernandez, Andrei Igoshev, Jo Taylor, David Sahnow, Logan Jones

Abstract: Observations utilizing the ultraviolet capabilities of the Cosmic Origin Spectrograph (COS) onboard the Hubble Space Telescope are of unique value to the astronomy community. Spectroscopy down to 900 A with COS has enabled new science areas. However, contrary to the situation at longer wavelengths, these observations are limited by detector background noise. The background correction currently app… ▽ More Observations utilizing the ultraviolet capabilities of the Cosmic Origin Spectrograph (COS) onboard the Hubble Space Telescope are of unique value to the astronomy community. Spectroscopy down to 900 A with COS has enabled new science areas. However, contrary to the situation at longer wavelengths, these observations are limited by detector background noise. The background correction currently applied by the standard calibration pipeline (CalCOS) is not optimized for faint targets, limiting the scientific value of low signal-to-noise observations. In this work we investigate a possible dependence of the variations of the dark rate in both segments of the COS far-ultraviolet (FUV) detector on time, detector high voltage (HV), and solar activity. Through our analysis we identified a number of detector states (on a configuration basis, e.g., HV and segment) characterizing the spatial distribution of dark counts, and created superdarks to be used in an optimized 2-dimensional (2D) background correction. We have developed and tested Another COS Dark Correction (ACDC), a dedicated pipeline to perform a 2D background correction based on statistical methods, producing background-corrected and flux-calibrated spectra. While our testing of ACDC showed an average improvement in S/N values of ~10%, in a few cases the improvements in S/N reached 60% across the whole wavelength range of individual segments. △ Less

Submitted 10 June, 2024; originally announced June 2024.

Comments: 12 pages, 6 figures, 3 tables, Accepted for publication in the Publications of the Astronomical Society of the Pacific

Bohr compactification and Chu duality of non-abelian locally compact groups

Authors: María V. Ferrer, S. Hernández

Abstract: The \emph{Bohr compactification} of an arbitrary topological group $G$ is defined as the group compactification $(bG,b)$ with the following universal property: for every continuous homomorphism $h$ from $G$ into a compact group $K$ there is a continuous homomorphism $h^{b}$ from $bG$ into $K$ extending $h$ in the sense that $h=h^b \circ b$. The Bohr compactification $(bG,b)$ is the unique (up to e… ▽ More The \emph{Bohr compactification} of an arbitrary topological group $G$ is defined as the group compactification $(bG,b)$ with the following universal property: for every continuous homomorphism $h$ from $G$ into a compact group $K$ there is a continuous homomorphism $h^{b}$ from $bG$ into $K$ extending $h$ in the sense that $h=h^b \circ b$. The Bohr compactification $(bG,b)$ is the unique (up to equivalence) largest compactification of $G$. Although, for locally compact Abelian groups, the Bohr compactification is a big monster, for non-Abelian groups the situation is much more interesting and it can be said that all options are possible. Here we are interested in locally compact groups whose Bohr compactification is \emph{small}. Among other results, we characterize when the Bohr the Bohr compactification of a locally compact group is topologically isomorphic to its Chu or unitary quasi-dual. Our results fixe some incorrect statements appeared in the literature. △ Less

Submitted 23 February, 2025; v1 submitted 4 May, 2024; originally announced May 2024.

The Baire property and precompact duality

Authors: M. Ferrer, S. Hernández, I. Sepúlveda, F. J. Trigos-Arrieta

Abstract: We prove that if $G$ is a totally bounded abelian group \st\ its dual group $\widehat{G}_p$ equipped with the finite-open topology is a Baire group, then every compact subset of $G$ must be finite. This solves an open question by Chasco, Domínguez and Tkachenko. {Among other consequences, we obtain an example of a group that is $g$-dense in its completion but is not $g$-barrelled. This solves a qu… ▽ More We prove that if $G$ is a totally bounded abelian group \st\ its dual group $\widehat{G}_p$ equipped with the finite-open topology is a Baire group, then every compact subset of $G$ must be finite. This solves an open question by Chasco, Domínguez and Tkachenko. {Among other consequences, we obtain an example of a group that is $g$-dense in its completion but is not $g$-barrelled. This solves a question proposed by Au$β$enhofer and Dikranjan.} △ Less

Submitted 4 May, 2024; originally announced May 2024.

NGC1856: Using machine learning techniques to uncover detailed stellar abundances from MUSE data

Authors: Randa Asa'd, S. Hernandez, Johina M. John, M. Alfaro-Cuello, Z. Wang, A. As'ad, A. Vasini, F. Matteucci

Abstract: We present the first application of the novel approach based on data-driven machine learning methods applied to Multi-Unit Spectroscopic Explorer (MUSE) field data to derive stellar abundances of star clusters. MUSE has been used to target more than 10,000 fields, and it is unique in its ability to study dense stellar fields such as stellar clusters providing spectra for each individual star. We u… ▽ More We present the first application of the novel approach based on data-driven machine learning methods applied to Multi-Unit Spectroscopic Explorer (MUSE) field data to derive stellar abundances of star clusters. MUSE has been used to target more than 10,000 fields, and it is unique in its ability to study dense stellar fields such as stellar clusters providing spectra for each individual star. We use MUSE data of the extragalactic young stellar cluster NGC 1856, located in the Large Magellanic Cloud (LMC). We present the individual stellar [Fe/H] abundance of 327 cluster members in addition to [Mg/Fe], [Si/Fe], [Ti/Fe], [C/Fe], [Ni/Fe], and [Cr/Fe] abundances of subsample sets. Our results match the LMC abundances obtained in the literature for [Mg/Fe], [Ti/Fe], [Ni/Fe], and [Cr/Fe]. This study is the first to derive [Si/Fe] and [C/Fe] abundances for this cluster. The revolutionary combination of integral-field spectroscopy and data-driven modeling will allow us to understand the chemical enrichment of star clusters and their host galaxies in greater detail expanding our understanding of galaxy evolution. △ Less

Submitted 25 April, 2024; v1 submitted 23 April, 2024; originally announced April 2024.

Comments: 18 pages

Embedding-based comparison of reaction networks of Wnt signaling

Authors: Bryan S. Hernandez, Patrick Vincent N. Lubenia, Eduardo R. Mendoza

Abstract: This work introduces a new method for comparing two reaction networks of the same or closely related systems through their embedded networks in terms of the shared set of species. Hence, we call this method the Common Species Embedded Networks (CSEN) analysis. Using this approach, we conduct a comparison of existing reaction networks associated with Wnt signaling models (Lee, Schmitz, MacLean, and… ▽ More This work introduces a new method for comparing two reaction networks of the same or closely related systems through their embedded networks in terms of the shared set of species. Hence, we call this method the Common Species Embedded Networks (CSEN) analysis. Using this approach, we conduct a comparison of existing reaction networks associated with Wnt signaling models (Lee, Schmitz, MacLean, and Feinberg) that we have identified. The analysis yields three important results for these Wnt models. First, the CSEN analysis of the Lee (mono-stationary) and Feinberg (multi-stationary) shows a strong similarity, justifying the study of the Feinberg model, which was a modified Lee model constructed to study an important network property called "concordance". It also challenge the absoluteness of discrimination of the models into mono-stationarity versus multi-stationarity, which is a main result of Maclean et al. (PNAS USA 2015). Second, the CSEN analysis provides evidence supporting a strong similarity between the Schmitz and MacLean models, as indicated by the "proximate equivalence" that we have identified. Third, the analysis underscores the absence of a comparable relationship between the Feinberg and MacLean models, highlighting distinctive differences between the two. Thus, our approach could be a useful tool to compare mathematical models of the same or closely related systems. △ Less

Submitted 1 April, 2024; originally announced April 2024.

Haro 11: The Spatially Resolved Lyman Continuum Sources

Authors: Lena Komarova, M. S. Oey, Svea Hernandez, Angela Adamo, Mattia Sirressi, Claus Leitherer, J. M. Mas-Hesse, Goran Ostlin, Edmund Hodges-Kluck, Arjan Bik, Matthew J. Hayes, Anne E. Jaskot, Daniel Kunth, Peter Laursen, Jens Melinder, T. Emil Rivera-Thorsen

Abstract: As the nearest confirmed Lyman continuum (LyC) emitter, Haro 11 is an exceptional laboratory for studying LyC escape processes crucial to cosmic reionization. Our new HST/COS G130M/1055 observations of its three star-forming knots now reveal that the observed LyC originates in Knots B and C, with $903 - 912~Å$ luminosities of $1.9\pm1.5 \times 10^{40}~\rm erg~s^{-1}$ and… ▽ More As the nearest confirmed Lyman continuum (LyC) emitter, Haro 11 is an exceptional laboratory for studying LyC escape processes crucial to cosmic reionization. Our new HST/COS G130M/1055 observations of its three star-forming knots now reveal that the observed LyC originates in Knots B and C, with $903 - 912~Å$ luminosities of $1.9\pm1.5 \times 10^{40}~\rm erg~s^{-1}$ and $0.9\pm0.7 \times 10^{40}~\rm erg~s^{-1}$, respectively. We derive local escape fractions $f_{\rm{esc, 912}} = 3.4\pm2.9\%$ and $5.1\pm4.3\%$ for Knots B and C, respectively. Our Starburst99 modeling shows dominant populations on the order of $\sim1-4$ Myr and $1-2\times10^7 \rm~M_\odot$ in each knot, with the youngest population in Knot B. Thus, the knot with the strongest LyC detection has the highest LyC production. However, LyC escape is likely less efficient in Knot B than in Knot C due to higher neutral gas covering. Our results therefore stress the importance of the intrinsic ionizing luminosity, and not just the escape fraction, for LyC detection. Similarly, the Ly$α$ escape fraction does not consistently correlate with LyC flux, nor do narrow Ly$α$ red peaks. High observed Ly$α$ luminosity and low Ly$α$ peak velocity separation, however, do correlate with higher LyC escape. Another insight comes from the undetected Knot A, which drives the Green Pea properties of Haro 11. Its density-bounded conditions suggest highly anisotropic LyC escape. Finally, both of the LyC-leaking Knots, B and C, host ultra-luminous X-ray sources (ULXs). While stars strongly dominate over the ULXs in LyC emission, this intriguing coincidence underscores the importance of unveiling the role of accretors in LyC escape and reionization. △ Less

Submitted 1 April, 2024; originally announced April 2024.

Comments: 22 pages, 5 figures. Accepted for publication in The Astrophysical Journal