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Motivated by phase transitions in combinatorial optimization problems, we define two kinds of geometry-preserving reductions between constraint satisfaction problems and other NP-search problems. We give a couple of examples and counterexamples for these reductions., Comment: In Proceedings FROM 2024, arXiv:2410.23020. An extended version is under preparation and will also be posted on arXiv

We investigate a signed version of the Hammersley process, a discrete process on words related to a property of integer sequences called heapability (Byers et al., ANALCO 2011). The specific version that we investigate corresponds to a version of this property for signed sequences. We give a characterization of the words that can appear as images the signed Hammersley process. In particular we show that the language of such words is the intersection of two deterministic one-counter languages.

We study the power of (competitive) algorithms with predictions in a multiagent setting. For this we introduce a multiagent version of the ski-rental problem. In this problem agents can collaborate by pooling resources to get a group license for some asset. If the license price is not met agents have to rent the asset individually for the day at a unit price. Otherwise the license becomes available forever to everyone at no extra cost. Our main contribution is a best-response analysis of a single-agent competitive algorithm that assumes perfect knowledge of other agents' actions (but no knowledge of its own renting time). We then analyze the setting when agents have a predictor for their own active time, yielding a tradeoff between robustness and consistency. We investigate the effect of using such a predictor in an equilibrium, as well as the new equilibria formed in this way.

We present the first volume-limited sample of spectroscopically confirmed hot subluminous stars out to 500 pc, defined using the accurate parallax measurements from the {\em Gaia} space mission data release 3 (DR3). The sample comprises a total of 397 members, with 305 ($\sim 77\%$) identified as hot subdwarf stars, including 83 newly discovered systems. Of these, we observe that 178 ($\sim58\%$) are hydrogen-rich sdBs, 65 are sdOBs ($\sim 21\%$), 32 are sdOs ($\sim 11\%$), and 30 are He-sdO/Bs ($\sim 10\%$). Among them, 48 ($\sim 16\%$) exhibit an infrared excess in their spectral energy distribution fits, suggesting a composite binary system. The hot subdwarf population is estimated to be 90\% complete, assuming that most missing systems are these composite binaries located within the main sequence (MS) in the \emph{Gaia} colour-magnitude diagram (CMD). The remaining sources in the sample include cataclysmic variables (CVs), blue horizontal branch stars (BHBs), hot white dwarfs (WDs), and MS stars. We derived the mid-plane density $\rho_{0}$ and scale height $\mathrm{h}_{z}$ for the non-composite hot subdwarf star population using a hyperbolic sechant profile (sech$^2$). The best-fit values are $\rho_{0}\,=\,5.17\pm 0.33 \times10^{-7}$ stars/pc$^{3}$ and $\mathrm{h}_{z} = 281 \pm 62$ pc. When accounting for the composite-colour hot subdwarfs and their estimated completeness, the mid-plane density increases to $\rho_{0}\,=\,6.15^ {+1.16}_{-0.53} \times10^{-7}$ stars/pc$^{3}$. This corrected space density is an order of magnitude lower than predicted by population synthesis studies, supporting previous observational estimates., Comment: Accepted for publication with A&A (permission has been granted by A&A to share this article on arXiv), 30 pages, 16 figures, 7 tables (4 + 3 appendices). The full table will be available in electronic form at the CDS

The Green Bank North Celestial Cap survey is one of the largest and most sensitive searches for pulsars and transient radio objects. Observations for the survey have finished; priorities have shifted toward long-term monitoring of its discoveries. In this study, we have developed a pipeline to handle large datasets of archival observations and connect them to recent, high-cadence observations taken using the Canadian Hydrogen Intensity Mapping Experiment (CHIME) telescope. This pipeline handles data for 128 pulsars and has produced measurements of spin, positional, and orbital parameters that connect data over observation gaps as large as 2000 days. We have also measured glitches in the timing residuals for five of the pulsars included and proper motion for 19 sources (13 new). We include updates to orbital parameters for 19 pulsars, including 9 previously unpublished binaries. For two of these binaries, we provide updated measurements of post-Keplerian binary parameters, which result in much more precise estimates of the total masses of both systems. For PSR J0509+3801, the much improved measurement of the Einstein delay yields much improved mass measurements for the pulsar and its companion, 1.399(6)\Msun and 1.412(6)\Msun, respectively. For this system, we have also obtained a measurement of the orbital decay due to the emission of gravitational waves: $\dot{P}_{\rm B} = -1.37(7)\times10^{-12}$, which is in agreement with the rate predicted by general relativity for these masses., Comment: accepted for publication in The Astrophysical Journal

In January 2020, a workshop was held at EMBL-EBI (Hinxton, UK) to discuss data requirements for deposition and validation of cryoEM structures, with a focus on single-particle analysis. The meeting was attended by 45 experts in data processing, model building and refinement, validation, and archiving of such structures. This report describes the workshop's motivation and history, the topics discussed, and consensus recommendations resulting from the workshop. Some challenges for future methods-development efforts in this area are also highlighted, as is the implementation to date of some of the recommendations., Comment: Outcomes of a wwPDB/EMDB workshop on cryoEM data management, deposition and validation

We prove upper and lower bounds for the threshold of the q-overlap-k-Exact cover problem. These results are motivated by the one-step replica symmetry breaking approach of Statistical Physics, and the hope of using an approach based on that of Mezard et al. (2005) to rigorously prove that for some values of the order parameter the overlap distribution of k-Exact Cover has discontinuous support., Comment: In Proceedings FROM 2023, arXiv:2309.12959

As the French, European and worldwide populations are aging, there is a strong interest for new systems that guarantee a reliable and privacy preserving home monitoring for frailty prevention. This work is a part of a global environmental audio analysis system which aims to help identification of Activities of Daily Life (ADL) through human and everyday life sounds recognition, speech presence and number of speakers detection. The focus is made on the number of speakers detection. In this article, we present how recent advances in sound processing and speaker diarization can improve the existing embedded systems. We study the performances of two new methods and discuss the benefits of DNN based approaches which improve performances by about 100%., Comment: JETSAN, Jun 2023, Aubervilliers & Paris, France

We report on the spectroscopic confirmation of 68 new bright ($G=13.5-17.2$ mag) and blue (pre-)white dwarfs (WDs). This finding has allowed us to almost double the number of the hottest ($T_{\mathrm{eff}} \geq 60$kK) known WDs brighter than $G=16$ mag. We increased the number of known ultra-high excitation (UHE) WDs by 20%, found one unambiguous close binary system consisting of one DA WD with an irradiated low-mass companion, one DAO, and one DOA WD that are likely in their transformation phase of becoming pure DA WDs, one rare, naked O(H) star, two DA and two DAO WDs with $T_{\mathrm{eff}}$ possibly in excess of 100kK, three new DOZ WDs, and three of our targets are central stars of (possible) planetary nebulae. Using non-local thermodynamic equilibrium models, we derived the atmospheric parameters of these stars and by fitting their spectral energy distribution we derived their radii, luminosities, and gravity masses. In addition, we derived their masses in the Kiel and Hertzsprung-Russell diagram (HRD). We find that Kiel, HRD, and gravity mass agree only in half of the cases. This is not unexpected and we attribute this to the neglect of metal opacities, possibly stratified atmospheres, as well as possible uncertainties of the parallax zero point determination. Furthermore, we carried out a search for photometric variability in our targets using archival data, finding that 26% of our targets are variable. This includes 15 new variable stars, with only one of them being clearly an irradiation effect system. Strikingly, the majority of the variable stars exhibit non-sinusoidal light-curve shapes, which are unlikely explained in terms of close binary systems. We propose that a significant fraction of all (not just UHE) WDs develop spots when entering the WD cooling phase. We suggest that this could be related to the on-set of weak magnetic fields and possibly diffusion., Comment: Accepted for publication in A&A

Planets orbiting close to hot stars experience intense extreme-ultraviolet radiation, potentially leading to atmosphere evaporation and to thermal dissociation of molecules. However, this extreme regime remains mainly unexplored due to observational challenges. Only a single known ultra-hot giant planet, KELT-9b, receives enough ultraviolet radiation for molecular dissociation, with a day-side temperature of ~4,600K. An alternative approach uses irradiated brown dwarfs as hot-Jupiter analogues. With atmospheres and radii similar to those of giant planets, brown dwarfs orbiting close to hot Earth-sized white-dwarf stars can be directly detected above the glare of the star. Here we report observations revealing an extremely irradiated low-mass companion to the hot white dwarf WD0032-317. Our analysis indicates a day-side temperature of ~8,000K, and a day-to-night temperature difference of ~6,000K. The amount of extreme-ultraviolet radiation (with wavelengths 100-912\r{A}) received by WD0032-317B is equivalent to that received by planets orbiting close to stars as hot as a late B-type stars, and about 5,600 times higher than that of KELT-9b. With a mass of ~75-88 Jupiter masses, this near-hydrogen-burning-limit object is potentially one of the most massive brown dwarfs known., Comment: Authors' version of the article published in Nature Astronomy (DOI https://doi.org/10.1038/s41550-023-02048-z)

Automatic Term Recognition is used to extract domain-specific terms that belong to a given domain. In order to be accurate, these corpus and language-dependent methods require large volumes of textual data that need to be processed to extract candidate terms that are afterward scored according to a given metric. To improve text preprocessing and candidate terms extraction and scoring, we propose a distributed Spark-based architecture to automatically extract domain-specific terms. The main contributions are as follows: (1) propose a novel distributed automatic domain-specific multi-word term recognition architecture built on top of the Spark ecosystem; (2) perform an in-depth analysis of our architecture in terms of accuracy and scalability; (3) design an easy-to-integrate Python implementation that enables the use of Big Data processing in fields such as Computational Linguistics and Natural Language Processing. We prove empirically the feasibility of our architecture by performing experiments on two real-world datasets.

Observations of individual massive stars, super-luminous supernovae, gamma-ray bursts, and gravitational-wave events involving spectacular black-hole mergers, indicate that the low-metallicity Universe is fundamentally different from our own Galaxy. Many transient phenomena will remain enigmatic until we achieve a firm understanding of the physics and evolution of massive stars at low metallicity (Z). The Hubble Space Telescope has devoted 500 orbits to observe 250 massive stars at low Z in the ultraviolet (UV) with the COS and STIS spectrographs under the ULLYSES program. The complementary ``X-Shooting ULLYSES'' (XShootU) project provides enhanced legacy value with high-quality optical and near-infrared spectra obtained with the wide-wavelength coverage X-shooter spectrograph at ESO's Very Large Telescope. We present an overview of the XShootU project, showing that combining ULLYSES UV and XShootU optical spectra is critical for the uniform determination of stellar parameters such as effective temperature, surface gravity, luminosity, and abundances, as well as wind properties such as mass-loss rates in function of Z. As uncertainties in stellar and wind parameters percolate into many adjacent areas of Astrophysics, the data and modelling of the XShootU project is expected to be a game-changer for our physical understanding of massive stars at low Z. To be able to confidently interpret James Webb Space Telescope (JWST) spectra of the first stellar generations, the individual spectra of low Z stars need to be understood, which is exactly where XShootU can deliver., Comment: Accepted in A&A - 35 Pages, 12 Figures, 4 Tables, 2 Large Tables

We report on the discovery of the companion star to the millisecond pulsar PSR J1835-3259B in the Galactic globular cluster NGC 6652. Taking advantage of deep photometric archival observations acquired through the Hubble Space Telescope in near-ultraviolet and optical bands, we identified a bright and blue object at a position compatible with that of the radio pulsar. The companion is located along the helium-core white dwarf cooling sequence and the comparison with binary evolution models provides a mass of $0.17 \pm 0.02~M_\odot$, a surface temperature of $11500\pm1900$ K and a very young cooling age of only $200\pm100$ Myr. The mass and the age of the companion are compatible with a progenitor star of about $0.87~M_{\odot}$, which started transferring mass to the primary during its evolution along the sub-giant branch and stopped during the early red giant branch phase. Combining together the pulsar mass function and the companion mass, we found that this system is observed at an almost edge-on orbit and hosts a neutron star with a mass of $1.44 \pm 0.06~M_\odot$, thus suggesting a highly non-conservative mass accretion phase. The young age of the WD companion is consistent with the scenario of a powerful, relatively young MSP indicated by the earlier detection of gamma-rays from this system., Comment: 11 pages, 7 figures, accepted for publication in ApJ

We study mechanism design with predictions for the obnoxious facility location problem. We present deterministic strategyproof mechanisms that display tradeoffs between robustness and consistency on segments, squares, circles and trees. All these mechanisms are actually group strategyproof, with the exception of the case of squares, where manipulations from coalitions of two agents exist. We prove that these tradeoffs are optimal in the 1-dimensional case.

We present timing solutions for 12 pulsars discovered in the Green Bank North Celestial Cap (GBNCC) 350 MHz pulsar survey, including six millisecond pulsars (MSPs), a double neutron star (DNS) system, and a pulsar orbiting a massive white dwarf companion. Timing solutions presented here include 350 and 820 MHz Green Bank Telescope data from initial confirmation and follow-up as well as a dedicated timing campaign spanning one year. PSR J1122$-$3546 is an isolated MSP, PSRs J1221$-$0633 and J1317$-$0157 are MSPs in black widow systems and regularly exhibit eclipses, and PSRs J2022+2534 and J2039$-$3616 are MSPs that can be timed with high precision and have been included in pulsar timing array experiments seeking to detect low-frequency gravitational waves. PSRs J1221$-$0633 and J2039$-$3616 have Fermi Large Area Telescope $\gamma$-ray counterparts and also exhibit significant $\gamma$-ray pulsations. We measure proper motion for three of the MSPs in this sample and estimate their space velocities, which are typical compared to those of other MSPs. We have detected the advance of periastron for PSR J1018$-$1523 and therefore measure the total mass of the double neutron star system, $m_{\rm tot}=2.3\pm0.3$ M$_{\odot}$. Long-term pulsar timing with data spanning more than one year is critical for classifying recycled pulsars, carrying out detailed astrometry studies, and shedding light on the wealth of information in these systems post-discovery., Comment: 21 pages, 5 figures, 7 tables

Almost periodicity has been considered in Formal Language Theory in connection with some topics in Symbolic Dynamics. In (P\u{a}un and Marcus, Bulletin of EATCS 53 (1994)) some problems concerning this property are raised. For instance it is asked whether there exists some almost periodic word $\alpha$ such that $Sub(\alpha)$, the set of its finite factors, is context-free non-regular. We answer negatively (even in a stronger form) this question, as well as discussing other related topics., Comment: Reconstructed source file of a paper originally published in 1995 in a volume currently without an online version (and with limited availability). Uploaded in order to ensure the online availability (and preservation) of the paper. This version faithfully reproduces the original, except for the addition of a note about the solution of Open Problem 3 and the correction of some minor typos

The stability of mass transfer is critical in determining pathways towards various kinds of compact binaries, such as compact main-sequence white-dwarf binaries, and transients, such as double white-dwarf mergers and luminous red novae. Despite its importance, only very few systematic studies of the stability of mass transfer exist. Using the 1D stellar evolution code MESA, we study the behaviour of mass-losing post-main-sequence donor stars with masses between $1 M_{\odot}$ and $8 M_{\odot}$ in binaries, without assuming that the donor star responds to mass loss adiabatically . We treat the accretor as a point mass, which we do not evolve, and assume the mass transfer is conservative. We find that the criterion that best predicts the onset of runaway mass transfer is based on the transition to an effectively adiabatic donor response to mass loss. We find that the critical mass ratio $q_{\rm qad} \sim 0.25$ for stars crossing the Hertzsprung gap, while for convective giants $q_{\rm qad}$ decreases from $\sim 1$ at the base of the RGB to $\sim 0.1$ at the the onset of thermal pulses on the AGB. An effectively adiabatic response of the donor star only occurs at a very high critical mass-transfer rate due to the short local thermal timescale in the outermost layers of a red giant. For $q > q_{\rm qad}$ mass transfer is self-regulated, but for evolved giants the resulting mass-transfer rates can be so high that the evolution becomes dynamical and/or the donor can overflow its outer lobe. Our results indicate that mass transfer is stable for a wider range of binary parameter space than typically assumed in rapid binary population synthesis and found in recent similar studies. Moreover, we find a systematic dependence of the critical mass ratio on the donor star mass and radius which may have significant consequences for predictions of post-mass-transfer populations., Comment: Accepted for publication in A&A. 21 pages, 10 figures, 2 tables

We describe the CZ Software Mentions dataset, a new dataset of software mentions in biomedical papers. Plain-text software mentions are extracted with a trained SciBERT model from several sources: the NIH PubMed Central collection and from papers provided by various publishers to the Chan Zuckerberg Initiative. The dataset provides sources, context and metadata, and, for a number of mentions, the disambiguated software entities and links. We extract 1.12 million unique string software mentions from 2.4 million papers in the NIH PMC-OA Commercial subset, 481k unique mentions from the NIH PMC-OA Non-Commercial subset (both gathered in October 2021) and 934k unique mentions from 3 million papers in the Publishers' collection. There is variation in how software is mentioned in papers and extracted by the NER algorithm. We propose a clustering-based disambiguation algorithm to map plain-text software mentions into distinct software entities and apply it on the NIH PubMed Central Commercial collection. Through this methodology, we disambiguate 1.12 million unique strings extracted by the NER model into 97600 unique software entities, covering 78% of all software-paper links. We link 185000 of the mentions to a repository, covering about 55% of all software-paper links. We describe in detail the process of building the datasets, disambiguating and linking the software mentions, as well as opportunities and challenges that come with a dataset of this size. We make all data and code publicly available as a new resource to help assess the impact of software (in particular scientific open source projects) on science.

One of the largest uncertainties in stellar evolutionary computations is the accuracy of the considered reaction rates. The 12C(alpha,gamma)16O reaction is particularly important for the study of low- and intermediate-mass stars as it determines the final C/O ratio in the core which influences the white dwarf cooling evolution. Thus, there is a need for a study of how the computations of white dwarfs and their progenitors that are made to date may be affected by the uncertainties of the 12C(alpha,gamma)16O reaction rates. In this work we compute fully evolutionary sequences using the MESA code with initial masses in the range of 0.90 <= Mi/Msun <= 3.05. We consider different adopted reaction rates, obtained from the literature, as well as the extreme limits within their uncertainties. As expected, we find that previous to the core helium burning stage there are no changes to the evolution of the stars. However, the subsequent stages are all affected by the uncertainties of the considered reaction rate. In particular, we find differences to the convective core mass during the core helium burning stage which may affect pulsation properties of subdwarfs, the number of thermal pulses during the asymptotic giant branch and trends between final oxygen abundance in the core and the progenitor masses of the remnant white dwarfs., Comment: 15 pages, 15 figures, 1 table

The Laser Interferometer Space Antenna (LISA) will be a transformative experiment for gravitational wave astronomy, and, as such, it will offer unique opportunities to address many key astrophysical questions in a completely novel way. The synergy with ground-based and space-born instruments in the electromagnetic domain, by enabling multi-messenger observations, will add further to the discovery potential of LISA. The next decade is crucial to prepare the astrophysical community for LISA's first observations. This review outlines the extensive landscape of astrophysical theory, numerical simulations, and astronomical observations that are instrumental for modeling and interpreting the upcoming LISA datastream. To this aim, the current knowledge in three main source classes for LISA is reviewed; ultracompact stellar-mass binaries, massive black hole binaries, and extreme or intermediate mass ratio inspirals. The relevant astrophysical processes and the established modeling techniques are summarized. Likewise, open issues and gaps in our understanding of these sources are highlighted, along with an indication of how LISA could help making progress in the different areas. New research avenues that LISA itself, or its joint exploitation with upcoming studies in the electromagnetic domain, will enable, are also illustrated. Improvements in modeling and analysis approaches, such as the combination of numerical simulations and modern data science techniques, are discussed. This review is intended to be a starting point for using LISA as a new discovery tool for understanding our Universe.

Helium-rich hot subdwarf stars of spectral type O (He-sdO) are considered prime candidates for stellar merger remnants. Such events should lead to the generation of strong magnetic fields. However, no magnetic He-sdO has yet been unambiguously discovered despite the high magnetic rate (20%) among white dwarf stars, the progeny of hot subdwarfs. Here we present the discovery of a strong magnetic field (B = 353 $\pm$ 10 kG) from Zeeman-split hydrogen, helium, and metal lines in the optical X-SHOOTER spectrum of an He-sdO and present the first spectroscopic analysis of any magnetic hot subdwarf. For this we used line-blanketed Tlusty non-local thermodynamic equilibrium models and assumed a simple homogeneous magnetic field. The derived atmospheric parameters $T_\mathrm{eff}$ = 44900 $\pm$ 1000 K and log g = 5.93 $\pm$ 0.15 are typical for He-sdO stars, while the star is less hydrogen-poor than most He-sdOs at log n(He)/n(H) = +0.28 $\pm$ 0.10. The star is a slow rotator ($v_\mathrm{rot}\sin i$ < 40 km s$^{-1}$). Its chemical composition is N-rich and C- and O-poor, and the Si and S abundances are close to solar. Combining the atmospheric parameters with Gaia parallax and photometry, the stellar radius and luminosity are found to be typical for He-sdOs and place the star on the helium main sequence in the Hertzsprung-Russell diagram. Its mass of $0.93^{+0.44}_{-0.30}$ $M_\odot$, although uncertain, appears to be remarkably high. The strong magnetic field along with the atmospheric parameters and metal abundances provide overwhelming evidence for the double-degenerate merger scenario., Comment: Accepted for publication as a letter in A&A