bluuebunny/crossref_metadata_2025_split huggingface dataset:
A closer look at low-mass post-AGB late thermal pulses
Authors: Lawlor T M 
Published: January 2023

ABSTRACT
Late thermal pulse (LTP) stellar evolution models experience a helium pulse that occurs following asymptotic giant branch (AGB) departure and causes a rapid looping evolution in the Hertzsprung–Russell (HR) diagram between the AGB and planetary nebula (PN) phase. The transient LTP phases only last decades to centuries while increasing and decreasing in temperature, luminosity, and size over orders of magnitude. LTP objects have often been described in the context of their more dramatic counterparts, very late thermal pulses (VLTPs). LTP stars do not evolve as quickly and do not become as hydrogen deficient as VLTP objects. They do not become conspicuous until after resembling a PN for thousands of years. We present stellar evolution calculations from the AGB to the PN phase for models over a range of metallicities from Z = 0.0015 to 0.03, and for masses 0.90, 1.2, and 2.0 ${\rm M_{\odot }}$. We focus in on our most dense series (1.2 ${\rm M_{\odot }}$, Z = 0.015) and designate a stratification of LTP types based on at what temperature they erupt, which may hint at the progenitor mass. We discuss one type that fits neither an LTP nor VLTP, which may offer an explanation for the star FG Sge. We present the time-scales during which LTP models heat up until reach peak helium-burning luminosity, during the rapid luminosity decline, and during the period of cooling and brightening, and we briefly discuss four LTP candidates.
Discovery of two cyclotron resonance scattering features in X-ray pulsar cen X-3 by Insight-HXMT
Authors: Yang W , Wang W , Liu Q , Chen X , Wu H J , Tian P F , Chen J S 
Published: January 2023

ABSTRACT
We present the results of the neutron star X-ray binary system Cen X-3 performed by Insight-HXMT with two observations during 2017 and 2018. During these two observations, the source reached a X-ray luminosity of ∼1038 erg s−1 from 2–105 keV. The analysis of the broadband X-ray spectrum reports the presence of two cyclotron resonance scattering features (CRSFs) with the fundamental line at ∼ 28 keV and the harmonic line at ∼47 keV. The multiple lines exist by fittings with different continuum models, like the absorbed negative and positive power-law with an exponential cutoff (NPEX) model and a power-law with high energy exponential cutoff model. This is the first time that both fundamental and harmonic lines are detected in Cen X-3. We also show evidence of two cyclotron lines in the phase-resolved spectrum of Cen X-3. The CRSF and continuum spectral parameters show evolution with the pulse profile, and the two line centroid energy ratio does not change significantly and locates in a narrow value range of 1.6−1.7 over the pulse phase. The implications of the discovering two cyclotron absorption features and phase-resolved spectral properties are discussed.
Reconstructing large-scale temperature profiles around z ∼ 6 quasars
Authors: Chen Huanqing , Croft Rupert A C , Gnedin Nickolay Y 
Published: January 2023

ABSTRACT
High-redshift quasars ionize He ii into He iii around them, heating the intergalactic medium in the process and creating large regions with elevated temperature. In this work, we demonstrate a method based on a convolutional neural network (CNN) to recover the spatial profile for T0, the temperature at the mean cosmic density, in quasar proximity zones. We train the neural network with synthetic spectra drawn from a Cosmic Reionization on Computers simulation. We discover that the simple CNN is able to recover the temperature profile with an accuracy of ≈1400 K in an idealized case of negligible observational uncertainties. We test the robustness of the CNN and discover that it is robust against the uncertainties in quasar host halo mass, quasar continuum, and ionizing flux. We also find that the CNN has good generality with regard to the hardness of quasar spectra. This shows that with noiseless spectra, one could use a simple CNN to distinguish gas inside or outside the He iii region created by the quasar. Because the size of the He iii region is closely related to the total quasar lifetime, this method has great potential in constraining the quasar lifetime on ∼Myr time-scales. However, noise poses a big problem for accuracy and could downgrade the accuracy to ≈2340 K even for very high signal-to-noise (≳50) spectra. Future studies are needed to reduce the error associated with noise to constrain the lifetimes of reionization epoch quasars with currently available data.
The impact of spurious collisional heating on the morphological evolution of simulated galactic discs
Authors: Wilkinson Matthew J , Ludlow Aaron D , Lagos Claudia del P , Fall S Michael , Schaye Joop , Obreschkow Danail 
Published: January 2023

ABSTRACT
We use a suite of idealized N-body simulations to study the impact of spurious heating of star particles by dark matter (DM) particles on the kinematics and morphology of simulated galactic discs. We find that spurious collisional heating leads to a systematic increase of the azimuthal velocity dispersion (σϕ) of stellar particles and a corresponding decrease in their mean azimuthal velocities ($\overline{v}_\phi$). The rate of heating is dictated primarily by the number of DM halo particles (or equivalently, by the DM particle mass at fixed halo mass) and by radial gradients in the local DM density along the disc; it is largely insensitive to the stellar particle mass. Galaxies within haloes resolved with fewer than ≈106 DM particles are particularly susceptible to spurious morphological evolution, irrespective of the total halo mass (with even more particles required to prevent heating of the galactic centre). Collisional heating transforms galactic discs from flattened structures into rounder spheroidal systems, causing them to lose rotational support in the process. It also affects the locations of galaxies in standard scaling relations that link their various properties: at fixed stellar mass, it increases the sizes of galaxies, and reduces their mean stellar rotation velocities and specific angular momenta. Our results urge caution when extrapolating simulated galaxy scaling relations to low masses where spurious collisional effects can bias their normalization, slope, and scatter.
Galaxy fields of LISA massive black hole mergers in a simulated universe
Authors: Lops Gaia , Izquierdo-Villalba David , Colpi Monica , Bonoli Silvia , Sesana Alberto , Mangiagli Alberto 
Published: January 2023

ABSTRACT
Laser Interferometer Space Antenna (LISA) will extend the search for gravitational waves (GWs) at $0.1\, {-}\, 100$ mHz where loud signals from coalescing binary black holes of $10^4 \, {-}\, 10^7\, \, \rm {M}_{\odot }$ are expected. Depending on their mass and luminosity distance, the uncertainty in the LISA sky-localization decreases from hundreds of deg2 during the inspiral phase to fractions of a deg2 after the merger. By using the semi-analytical model L-Galaxies applied to the Millennium-I merger trees, we generate a simulated universe to identify the hosts of $z\, {\le }\, 3$ coalescing binaries with total mass of $3\, {\times }\, 10^{5}$, $3\, {\times }\, 10^6$, and $3\, {\times }\, 10^7\, \rm {M}_{\odot }$, and varying mass ratio. We find that, even at the time of merger, the number of galaxies around the LISA sources is too large (${\gtrsim }\, 10^2$) to allow direct host identification. However, if an X-ray counterpart is associated to the GW sources at $z\, {&lt; }\, 1$, all LISA fields at merger are populated by ${\lesssim }\, 10$ active galactic nuclei (AGNs) emitting above ${\sim }\, 10^{-17} \, \rm erg\, cm^{-2}\, s^{-1}$. For sources at higher redshifts, the poorer sky-localization causes this number to increase up to ${\sim }\, 10^3$. Archival data from eRosita will allow discarding ${\sim }\, 10{{\ \rm per\ cent}}$ of these AGNs, being too shallow to detect the dim X-ray luminosity of the GW sources. Inspiralling binaries in an active phase with masses ${\lesssim }\, 10^6\, \rm {M}_{\odot }$ at $z\, {\le }\, 0.3$ can be detected, as early as 10 h before the merger, by future X-ray observatories in less than a few minutes. For these systems, ${\lesssim }\, 10$ AGNs are within the LISA sky-localization area. Finally, the LISA-Taiji network would guarantee the identification of an X-ray counterpart 10 h before merger for all binaries at $z\, {\lesssim }\, 1$.
Optical/γ-ray blazar flare correlations: understanding the high-energy emission process using ASAS-SN and Fermi light curves
Authors: de Jaeger T , Shappee B J , Kochanek C S , Hinkle J T , Garrappa S , Liodakis I , Franckowiak A , Stanek K Z , Beacom J F , Prieto J L 
Published: January 2023

ABSTRACT
Using blazar light curves from the optical All-Sky Automated Survey for Supernovae (ASAS-SN) and the γ-ray Fermi-LAT telescope, we performed the most extensive statistical correlation study between both bands, using a sample of 1180 blazars. This is almost an order of magnitude larger than other recent studies. Blazars represent more than 98 per cent of the AGNs detected by Fermi-LAT and are the brightest γ-ray sources in the extragalactic sky. They are essential for studying the physical properties of astrophysical jets from central black holes. However, their γ-ray flare mechanism is not fully understood. Multiwavelength correlations help constrain the dominant mechanisms of blazar variability. We search for temporal relationships between optical and γ-ray bands. Using a Bayesian Block Decomposition, we detect 1414 optical and 510 γ-ray flares, we find a strong correlation between both bands. Among all the flares, we find 321 correlated flares from 133 blazars, and derive an average rest-frame time delay of only 1.1$_{-8.5}^{+7.1}$ d, with no difference between the flat-spectrum radio quasars, BL Lacertae-like objects or low, intermediate, and high-synchrotron peaked blazar classes. Our time-delay limit rules out the hadronic proton-synchrotron model as the driver for non-orphan flares and suggests a leptonic single-zone model. Limiting our search to well-defined light curves and removing 976 potential but unclear ‘orphan’ flares, we find 191 (13 per cent) and 115 (22 per cent) clear ‘orphan’ optical and γ-ray flares. The presence of ‘orphan’ flares in both bands challenges the standard one-zone blazar flare leptonic model and suggests multizone synchrotron sites or a hadronic model for some blazars.
Tracking the origin of black holes with the stochastic gravitational wave background popcorn signal
Authors: Braglia Matteo , García-Bellido Juan , Kuroyanagi Sachiko 
Published: January 2023

ABSTRACT
Unresolved sources of gravitational waves (GWs) produced by the merger of a binary of black holes at cosmological distances combine into a stochastic background. Such a background is in the continuous or popcorn regime, depending on whether the GW rate is high enough so that two or more events overlap in the same frequency band. These two regimes respectively correspond to large and small values of the so-called duty cycle. We study the detection regime of the background in models of primordial black holes (PBHs) and compare it to the one produced by black holes of stellar origin. Focusing on ground-based detectors, we show that the duty cycle of the PBH-origin background is larger than that of astrophysical black holes because of differences in their mass function and the merger rate. Our study opens up the possibility to learn about the primordial or astrophysical nature of black hole populations by examining the statistical properties of the stochastic background.
Pervasive Selection for Clinically Relevant Resistance and Media Adaptive Mutations at Very Low Antibiotic Concentrations
Authors: Pereira Catia , Warsi Omar M , Andersson Dan I 
Published: January 2023

Abstract
Experimental evolution studies have shown that weak antibiotic selective pressures (i.e., when the antibiotic concentrations are far below the minimum inhibitory concentration, MIC) can select resistant mutants, raising several unanswered questions. First, what are the lowest antibiotic concentrations at which selection for de novo resistance mutations can occur? Second, with weak antibiotic selections, which other types of adaptive mutations unrelated to the antibiotic selective pressure are concurrently enriched? Third, are the mutations selected under laboratory settings at subMIC also observed in clinical isolates? We addressed these questions using Escherichia coli populations evolving at subMICs in the presence of either of four clinically used antibiotics: fosfomycin, nitrofurantoin, tetracycline, and ciprofloxacin. Antibiotic resistance evolution was investigated at concentrations ranging from 1/4th to 1/2000th of the MIC of the susceptible strain (MICsusceptible). Our results show that evolution was rapid across all the antibiotics tested, and selection for fosfomycin- and nitrofurantoin-resistant mutants was observed at a concentration as low as 1/2000th of MICsusceptible. Several of the evolved resistant mutants showed increased growth yield and exponential growth rates, and outcompeted the susceptible ancestral strain in the absence of antibiotics as well, suggesting that adaptation to the growth environment occurred in parallel with the selection for resistance. Genomic analysis of the resistant mutants showed that several of the mutations selected under these conditions are also found in clinical isolates, demonstrating that experimental evolution at very low antibiotic levels can help in identifying novel mutations that contribute to bacterial adaptation during subMIC exposure in real-life settings.
Influence of chain length and branching on poly(ADP-ribose)–protein interactions
Authors: Löffler Tobias , Krüger Annika , Zirak Peyman , Winterhalder Martin J , Müller Anna-Lena , Fischbach Arthur , Mangerich Aswin , Zumbusch Andreas 
Published: January 2023

Abstract
Hundreds of proteins interact with poly(ADP-ribose) (PAR) via multiple PAR interaction motifs, thereby regulating their physico-chemical properties, sub-cellular localizations, enzymatic activities, or protein stability. Here, we present a targeted approach based on fluorescence correlation spectroscopy (FCS) to characterize potential structure-specific interactions of PAR molecules of defined chain length and branching with three prime PAR-binding proteins, the tumor suppressor protein p53, histone H1, and the histone chaperone APLF. Our study reveals complex and structure-specific PAR–protein interactions. Quantitative Kd values were determined and binding affinities for all three proteins were shown to be in the nanomolar range. We report PAR chain length dependent binding of p53 and H1, yet chain length independent binding of APLF. For all three PAR binders, we found a preference for linear over hyperbranched PAR. Importantly, protein- and PAR-structure-specific binding modes were revealed. Thus, while the H1-PAR interaction occurred largely on a bi-molecular 1:1 basis, p53—and potentially also APLF—can form complex multivalent PAR–protein structures. In conclusion, our study gives detailed and quantitative insight into PAR–protein interactions in a solution-based setting at near physiological buffer conditions. The results support the notion of protein and PAR-structure-specific binding modes that have evolved to fit the purpose of the respective biochemical functions and biological contexts.
Human DNA ligases I and III have stand-alone end-joining capability, but differ in ligation efficiency and specificity
Authors: McNally Justin R , Ames Amanda M , Admiraal Suzanne J , O’Brien Patrick J 
Published: January 2023

Abstract
Double-strand DNA breaks (DSBs) are toxic to cells, and improper repair can cause chromosomal abnormalities that initiate and drive cancer progression. DNA ligases III and IV (LIG3, LIG4) have long been credited for repair of DSBs in mammals, but recent evidence suggests that DNA ligase I (LIG1) has intrinsic end-joining (EJ) activity that can compensate for their loss. To test this model, we employed in vitro biochemical assays to compare EJ by LIG1 and LIG3. The ligases join blunt-end and 3′-overhang-containing DNA substrates with similar catalytic efficiency, but LIG1 joins 5′-overhang-containing DNA substrates ∼20-fold less efficiently than LIG3 under optimal conditions. LIG1-catalyzed EJ is compromised at a physiological concentration of Mg2+, but its activity is restored by increased molecular crowding. In contrast to LIG1, LIG3 efficiently catalyzes EJ reactions at a physiological concentration of Mg2+ with or without molecular crowding. Under all tested conditions, LIG3 has greater affinity than LIG1 for DNA ends. Remarkably, LIG3 can ligate both strands of a DSB during a single binding encounter. The weaker DNA binding affinity of LIG1 causes significant abortive ligation that is sensitive to molecular crowding and DNA terminal structure. These results provide new insights into mechanisms of alternative nonhomologous EJ.
Observation of dark edge states in parity-time-symmetric quantum dynamics
Authors: Xue Peng , Qiu Xingze , Wang Kunkun , Sanders Barry C , Yi Wei 
Published: January 2023

ABSTRACT
Topological edge states arise in non-Hermitian parity-time ($\mathcal {PT}$)-symmetric systems, and manifest themselves as bright or dark edge states, depending on the imaginary components of their eigenenergies. As the spatial probabilities of dark edge states are suppressed during the non-unitary dynamics, it is a challenge to observe them experimentally. Here we report the experimental detection of dark edge states in photonic quantum walks with spontaneously broken $\mathcal {PT}$ symmetry, thus providing a complete description of the topological phenomena therein. We experimentally confirm that the global Berry phase in $\mathcal {PT}$-symmetric quantum-walk dynamics unambiguously defines topological invariants of the system in both the $\mathcal {PT}$-symmetry-unbroken and -broken regimes. Our results establish a unified framework for characterizing topology in $\mathcal {PT}$-symmetric quantum-walk dynamics, and provide a useful method to observe topological phenomena in $\mathcal {PT}$-symmetric non-Hermitian systems in general.
The smallest in the deepest: the enigmatic role of viruses in the deep biosphere
Authors: Cai Lanlan , Weinbauer Markus G , Xie Le , Zhang Rui 
Published: January 2023

ABSTRACT
It is commonly recognized that viruses control the composition, metabolism, and evolutionary trajectories of prokaryotic communities, with resulting vital feedback on ecosystem functioning and nutrient cycling in a wide range of ecosystems. Although the deep biosphere has been estimated to be the largest reservoir for viruses and their prokaryotic hosts, the biology and ecology of viruses therein remain poorly understood. The deep virosphere is an enigmatic field of study in which many critical questions are still to be answered. Is the deep virosphere simply a repository for deeply preserved, non-functioning virus particles? Or are deep viruses infectious agents that can readily infect suitable hosts and subsequently shape microbial populations and nutrient cycling? Can the cellular content released by viral lysis, and even the organic structures of virions themselves, serve as the source of bioavailable nutrients for microbial activity in the deep biosphere as in other ecosystems? In this review, we synthesize our current knowledge of viruses in the deep biosphere and seek to identify topics with the potential for substantial discoveries in the future.
Leaded aviation gasoline exposure risk and child blood lead levels
Authors: Zahran Sammy , Keyes Christopher , Lanphear Bruce 
Published: January 2023

Abstract
Lead-formulated aviation gasoline (avgas) is the primary source of lead emissions in the United States today, consumed by over 170,000 piston-engine aircraft (PEA). The U.S. Environmental Protection Agency (EPA) estimates that four million people reside within 500m of a PEA-servicing airport. The disposition of avgas around such airports may be an independent source of child lead exposure. We analyze over 14,000 blood lead samples of children (≤5 y of age) residing near one such airport—Reid-Hillview Airport (RHV) in Santa Clara County, California. Across an ensemble of tests, we find that the blood lead levels (BLLs) of sampled children increase in proximity to RHV, are higher among children east and predominantly downwind of the airport, and increase with the volume of PEA traffic and quantities of avgas sold at the airport. The BLLs of airport-proximate children are especially responsive to an increase in PEA traffic, increasing by about 0.72 μg/dL under periods of maximum PEA traffic. We also observe a significant reduction in child BLLs from a series of pandemic-related interventions in Santa Clara County that contracted PEA traffic at the airport. Finally, we find that children’s BLLs increase with measured concentrations of atmospheric lead at the airport. In support of the scientific adjudication of the EPAs recently announced endangerment finding, this in-depth case study indicates that the deposition of avgas significantly elevates the BLLs of at-risk children.
A Comprehensive conceptual and computational dynamics framework for autonomous regeneration of form and function in biological organisms
Authors: Samarasinghe Sandhya , Minh-Thai Tran Nguyen 
Published: January 2023

AbstractIn biology, regeneration is a mysterious phenomenon that has inspired self-repairing systems, robots, and biobots. It is a collective computational process whereby cells communicate to achieve an anatomical set point and restore original function in regenerated tissue or the whole organism. Despite decades of research, the mechanisms involved in this process are still poorly understood. Likewise, the current algorithms are insufficient to overcome this knowledge barrier and enable advances in regenerative medicine, synthetic biology, and living machines/biobots. We propose a comprehensive conceptual framework for the engine of regeneration with hypotheses for the mechanisms and algorithms of stem cell-mediated regeneration that enables a system like the planarian flatworm to fully restore anatomical (form) and bioelectric (function) homeostasis from any small- or large-scale damage. The framework extends the available regeneration knowledge with novel hypotheses to propose collective intelligent self-repair machines with multi-level feedback neural control systems driven by somatic and stem cells. We computationally implemented the framework to demonstrate the robust recovery of both form and function (anatomical and bioelectric homeostasis) in an in silico worm that, in a simple way, resembles the planarian. In the absence of complete regeneration knowledge, the framework contributes to understanding and generating hypotheses for stem cell mediated form and function regeneration, which may help advance regenerative medicine and synthetic biology. Further, as our framework is a bio-inspired and bio-computing self-repair machine, it may be useful for building self-repair robots/biobots and artificial self-repair systems.