bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stellar collisions in globular clusters: the origin of multiple stellar populations
Authors: Kravtsov Valery , Dib Sami , Calderón Francisco A , Belinchón José Antonio 
Published: March 2022

ABSTRACT
Two generations of stars, G1 and G2, typically populate Galactic globular clusters (GCs). The origin of G2 stars is unclear. We uncover two empirical dependencies between GC characteristics, which can be explained by the formation of G2 main-sequence (MS) stars due to collision/merging of their primordial counterparts (G1). A similar genesis of both G2 stars and peculiar objects like low-mass X-ray binaries and millisecond pulsars is also implied. Indeed, we find a significant (at a confidence level ${\gt} 99.9{{\ \rm per\ cent}}$) anticorrelation between the fraction of G1 red giants (NG1/Ntot) and stellar encounter rates among 51 GCs. Moreover, a Milky Way-like initial mass function requires at least ∼50 per cent of MS stars located in the mass range [0.1–0.5] M⊙. Unlike cluster mass loss, stellar collisions/merging retain these G1 stars by converting them into more massive G2 ones, with mainly MMS &gt; 0.5 M⊙. This process coupled with a decreasing relative mass loss with increasing GC masses implies a smaller (NG1/Ntot) in more massive GCs with a shallower present-day mass function. From data for 35 GCs, we find that such an anticorrelation is significant at 98.3 per cent confidence level (Spearman’s correlation) for the 12 most massive GCs (MGC &gt; 105.3 M⊙) and it is at a confidence level of 89 per cent for the 12 least massive GCs (MGC &lt; 105.1 M⊙). Other fractions of G1 and G2 stars observed at the bottom of the MS as compared with the red giant branch in a few GCs are consistent with the scenario proposed.
On the kinematic cosmic dipole tension
Authors: Dalang Charles , Bonvin Camille 
Published: March 2022

ABSTRACT
Our motion through the Universe generates a dipole in the temperature anisotropies of the Cosmic Microwave Background (CMB) and also in the angular distribution of sources. If the cosmological principle is valid, these two dipoles are directly linked, such that the amplitude of one determines that of the other. However, it is a longstanding problem that number counts of radio sources and of quasars at low and intermediate redshifts exhibit a dipole that is well aligned with that of the CMB but with about twice the expected amplitude, leading to a tension reaching up to 4.9σ. In this paper, we revisit the theoretical derivation of the dipole in the sources number counts, explicitly accounting for the redshift evolution of the population of sources. We argue that if the spectral index and magnification bias of the sources vary with redshift, the standard theoretical description of the dipole may be inaccurate. We provide an alternative expression which does not depend on the spectral index, but instead on the time evolution of the population of sources. We then determine the values that this evolution rate should have in order to remove the tension with the CMB dipole.
The impact hazard of near-Sun comets
Authors: Neslušan Luboš , Tomko Dušan 
Published: March 2022

ABSTRACT
There are several groups of comets with perihelion near the solar surface known. Of these, the Marsden and Kracht groups move in orbits situated in a spatial corridor of the daytime Arietid meteoroid stream. The orbits of comets of the Meyer group are not very different from those of the Marsden and Kracht groups; for the purpose of our study, we thus consider a common Meyer–Marsden–Kracht (MMK) group. Since Arietids pass close to the Earth’s orbit, comets of the MMK group must also do so. We study the close approaches of the orbits of these comets with regard to the proximity of the orbit of our planet and estimate an impact hazard. We found a concentration of approaches within an interval of solar longitude from ∼72○–84○ (between June 2 and June 15). The mean time between two collisions of an MMK comet and Earth is estimated to be one to two million years, assuming a steady state during that period.
Impact of a quasi-molecular mechanism of cosmological recombination on the population of the 2s-level of hydrogen
Authors: Kereselidze Tamaz , Noselidze Irakli , Khetsuriani Shota 
Published: March 2022

ABSTRACT
The population of the 2s-level of hydrogen formed in the early Universe is studied within a standard and a non-standard quasi-molecular mechanism of recombination. We demonstrate that, if hydrogen molecular ion $H_2^+$ temporarily formed during a collision directly dissociates into a hydrogen atom and a proton, both mechanisms of recombination lead to the same probabilities of population. These probabilities differ significantly, however, when attractive quasi-molecular channels are uninvolved and only repulsive channels remain in the treatment. The probabilities of the direct and indirect radiative transitions into the 2s-level of hydrogen are evaluated. The dominant process in the population of 2s-level of hydrogen is the direct free–bound radiative transition.
On the stability of shocks in isothermal black hole accretion discs
Authors: Hester Eric W , Vasil Geoffrey M , Wechselberger Martin 
Published: March 2022

ABSTRACT
Most black holes possess accretion discs. Models of such discs inform observations and constrain the properties of the black holes and their surrounding medium. Here, we study shocks in a thin isothermal black hole accretion flow. Modelling infinitesimal viscosity allows the use of multiple-scales matched asymptotic methods. We thus derive the first explicit calculations of isothermal shock stability. We find that the inner shock is always unstable, and the outer shock is always stable. The growth/decay rates of perturbations depend only on an effective potential and the incoming–outgoing flow difference at the shock location. We give a prescription of accretion regimes in terms of angular momentum and black hole radius. Accounting for viscous angular momentum dissipation implies unstable outer shocks in much of parameter space, even for realistic viscous Reynolds numbers of the order ≈1020.
Extracting the 21-cm power spectrum and the reionization parameters from mock data sets using artificial neural networks
Authors: Choudhury Madhurima , Datta Abhirup , Majumdar Suman 
Published: March 2022

ABSTRACT
Detection of the H i 21-cm power spectrum is one of the key science drivers of several ongoing and upcoming low-frequency radio interferometers. However, the major challenge in such observations come from bright foregrounds, whose accurate removal or avoidance is key to the success of these experiments. In this work, we demonstrate the use of artificial neural networks (ANNs) to extract the H i 21-cm power spectrum from synthetic data sets and extract the reionization parameters from the H i 21-cm power spectrum. For the first time, using a suite of simulations, we present an ANN-based framework capable of extracting the H i signal power spectrum directly from the total observed sky power spectrum (which contains the 21-cm signal, along with the foregrounds and effects of the instrument). We have used a combination of two ANNs sequentially. In the first step, ANN1 predicts the 21-cm power spectrum directly from foreground corrupted synthetic data sets. In the second step, ANN2 predicts the reionization parameters from the predicted H i power spectra from ANN1. The two-step ANN framework can be used as an alternative method to extract the 21-cm power spectrum and the reionization parameters directly from foreground dominated data sets. Our ANN-based framework is trained at a redshift of 9.01, and for $\boldsymbol {k}$ modes in the range, $\rm {0.17\lt {\boldsymbol {k}}\lt 0.37~Mpc^{-1}}$. We have tested the network’s performance with mock data sets corrupted with thermal noise corresponding to 1080 h of observations of the SKA-1 LOW and HERA. We have recovered the H i power spectra from foreground dominated synthetic data sets, with an accuracy of $\approx 95{\!-\!}99{{\ \rm per\ cent}}$. We have achieved an accuracy of $\approx ~81{\!-\!}90{{\ \rm per\ cent}}$ and $\approx ~50{\!-\!}60{{\ \rm per\ cent}}$ for the predicted reionization parameters, for test sets corrupted with thermal noise corresponding to the SKA-1 LOW and HERA, respectively.
The relation between X-ray and ultraviolet variability of quasars
Authors: Sou Hao , Wang Jun-Xian , Xie Zhang-Liang , Kang Wen-Yong , Cai Zhen-Yi 
Published: March 2022

ABSTRACT
The relation between X-ray and UV/optical variability in AGNs has been explored in many individual sources, however a large sample study is yet absent. Through matching the XMM-Newton serendipitous X-ray and UV source catalogs with SDSS quasars, we build a sample of 802 epoch-pairs of 525 quasars showing clear variability in logFX − logFUV space. After correcting for the effect of photometric noise, we find 35.6 ± 2.1 per cent of the epoch-pairs show asynchronous variability between X-ray and UV (brightening in one band but dimming in the other). This indicates only in 28.8 ± 4.2 per cent of the epoch-pairs the X-ray and UV variability are intrinsically coordinated. The variability synchronicity exhibits no dependence on physical parameters of quasars or the time lag of the epoch-pairs, except for stronger variability tends to have stronger synchronicity. Switches between synchronous and asynchronous variability are also seen in individual sources. The poor coordination clearly contradicts both the X-ray reprocessing model and the accretion rate variation model for AGN variability. The ratios of the observed X-ray variability amplitude to that in UV span a broad range and peak at ∼2. The dominant fraction of the ratios appear too small to be attributed to X-ray reprocessing, and too large for accretion rate variation. The inhomogeneous disc model which incorporates both X-ray and UV/optical variability in AGNs is favoured by the observed stochastic relation between X-ray and UV variations.
The large landscape of supernova, GRB, and cocoon interactions
Authors: De Colle Fabio , Kumar Pawan , Hoeflich Peter 
Published: March 2022

ABSTRACTLong gamma-ray bursts (LGRBs) are associated to the collapse of a massive star and the formation of a relativistic jet. As the jet propagates through the star, it forms an extended, hot cocoon. The dynamical evolution of the jet/cocoon system and its interaction with the environment has been studied extensively both analytically and numerically. On the other hand, the role played by the supernova (SN) explosion associated with LGRBs in determining the outcome of the system has been barely considered. In this paper, we discuss the large landscape of outcomes resulting from the interaction of the SN, jet, and cocoon. We show that the outcome depends mainly on three time-scales: the times for the cocoon and SN shock wave to break through the surface of the progenitor star, and the time needed for the cocoon to engulf completely the progenitor star. The delay between the launch of the SN shock moving through the progenitor star and the jet can be related to these three time-scales. Depending on the ordering of these time-scales, the jet-cocoon might propagate inside the SN ejecta or the other way around, and the outcome for the properties of the explosion would be different. We discuss the imprint of the complex interaction between the jet-cocoon and the SN shock on the emergent thermal and non-thermal radiation.
Some aspects of rotation and magnetic-field morphology in the infrared dark cloud G34.43+00.24
Authors: Vahdanian Hamed , Nejad-Asghar Mohsen 
Published: March 2022

ABSTRACTThe infrared dark clouds (IRDCs) are molecular clouds with relatively greater values in their magnetic-field strengths. For example, the IRDC G34.43+00.24 (G34) has magnetic-field strength of the order of a few hundred micro-Gauss. In this study, we investigate if the dynamic motions of charged particles in an IRDC such as G34 can produce this magnetic-field strength inside it. The observations show that the line-of-sight velocity of G34 has global gradient. We assume that the measured global velocity gradient can correspond to the cloud rotation. We attribute a large-scale current density to this rotating cloud by considering a constant value for the incompleteness of charge neutrality and the velocity differences between the positive and negative particles with very low ionization fractions. We use the numerical package fishpack to obtain the magnetic-field strength and its morphology on the plane-of-sky within G34. The results show that the magnetic-field strengths are of the order of several hundred micro-Gauss, and its morphology in the plane-of-sky is somewhat consistent with the observational results. We also obtain the relationship between magnetic-field strength and density in G34. The results show that with increasing density, the magnetic-field strength increases approximately as a power-law function. The amount of power is approximately equal to 0.45, which is suitable for molecular clouds with strong magnetic fields. Therefore, we can conclude that the dynamical motion of IRDCs, and especially their rotations, can amplify the magnetic-field strengths within them.
Gattaca: Base-Pair Resolution Mutation Tracking for Somatic Evolution Studies using Agent-based Models
Authors: Schenck Ryan O. , Brosula Gabriel , West Jeffrey , Leedham Simon , Shibata Darryl , Anderson Alexander R.A. 
Published: March 2022

Abstract
Research over the past two decades has made substantial inroads into our understanding of somatic mutations. Recently, these studies have focused on understanding their presence in homeostatic tissue. In parallel, agent-based mechanistic models have emerged as an important tool for understanding somatic mutation in tissue; yet no common methodology currently exists to provide base-pair resolution data for these models. Here, we present Gattaca as the first method for introducing and tracking somatic mutations at the base-pair resolution within agent-based models that typically lack nuclei. With nuclei that incorporate human reference genomes, mutational context, and sequence coverage/error information, Gattaca is able to realistically evolve sequence data, facilitating comparisons between in silico cell tissue modeling with experimental human somatic mutation data. This user-friendly method, incorporated into each in silico cell, allows us to fully capture somatic mutation spectra and evolution.
DNA metabarcoding reveals broad woodpecker diets in fire-maintained forests
Authors: Stillman Andrew N , Caiafa Marcos V , Lorenz Teresa J , Jusino Michelle A , Tingley Morgan W 
Published: March 2022

Abstract
Ecological disturbance is a key agent shaping the spatial and temporal landscape of food availability. In forests of western North America, disturbance from fire can lead to resource pulses of deadwood-associated arthropods that provide important prey for woodpeckers. Although the foraging strategies among woodpecker species often demonstrate pronounced differences, little is known about the ways in which woodpeckers exploit and partition prey in disturbed areas. In this study, we employed DNA metabarcoding to characterize and compare the arthropod diets of 4 woodpecker species in Washington and California, USA—Black-backed Woodpecker (Picoides arcticus), Hairy Woodpecker (Dryobates villosus), Northern Flicker (Colaptes auratus), and White-headed Woodpecker (Dryobates albolarvatus)—primarily using nestling fecal samples from burned forests 1–13 years postfire. Successful sequencing from 78 samples revealed the presence of over 600 operational taxonomic units (OTUs) spanning 32 arthropod orders. The nestling diets of two species in particular—Northern Flicker and Black-backed Woodpecker—proved to be much broader than previous observational studies suggest. Northern Flicker nestlings demonstrated significantly higher diet diversity compared to other focal species, all of which displayed considerable overlap in diversity. Wood-boring beetles, which colonize dead and dying trees after fire, were particularly important diet items for Black-backed, Hairy, and White-headed woodpeckers. Diet composition differed among species, and diets showed limited differences between newer (≤5 yr) and older (&gt;5 yr) postfire forests. Our results show mixed evidence for dietary resource partitioning, with three of the four focal species exhibiting relatively high diet overlap, perhaps due to the pulsed subsidy of deadwood-associated arthropods in burned forests. Woodpeckers are frequently used as management indicator species for forest health, and our study provides one of the first applications of DNA metabarcoding to build a more complete picture of woodpecker diets.
Extensions and limitations of MacArthur (1958): A review of ecological and evolutionary approaches to competition and diet in the New World wood warblers (Parulidae)
Authors: Sherry Thomas W , Kent Cody M 
Published: March 2022

AbstractThe extent to which interspecific competition structures species interactions and coexistence within communities, and the relevant mechanisms, are still debated. We focus on New World wood warblers (Parulidae), beginning with Robert MacArthur’s iconic 1958 paper in which he shows how subtle foraging behaviors, purportedly linked to dietary differences, within spruce trees contribute to the coexistence of 5 spruce-woods warbler species. MacArthur coined the phrase “resource partitioning”, and profoundly impacted the field of Ecology for subsequent decades in diverse ways. To understand what MacArthur got right and what he missed, we reviewed both ecological and evolutionary approaches to questions of the origin and coexistence of competing species in the context of diet. We argue that an important, underappreciated, mechanism of competition among coexisting migratory warbler species, particularly in winter, is diffuse exploitation competition, based in part on our own studies of warbler diets in relation to foraging behavior, substrate use, bird morphology, and other traits. Our review and synthesis of interspecific competition and coexistence in warblers have important consequences, including our questioning of the importance and effectiveness of resource partitioning in birds. We also suggest a novel hypothesis for the success of warblers today in the Caribbean and other habitats, beginning with their relatively recent adaptive radiation and the ecological opportunity on Caribbean islands.
An artificial host system enables the obligate parasite Cuscuta campestris to grow and reproduce in vitro
Authors: Bernal-Galeano Vivian , Beard Keely , Westwood James H 
Published: March 2022

Abstract
Cuscuta campestris is an obligate parasitic plant that requires a host to complete its life cycle. Parasite–host connections occur via a haustorium, a unique organ that acts as a bridge for the uptake of water, nutrients, and macromolecules. Research on Cuscuta is often complicated by host influences, but comparable systems for growing the parasite in the absence of a host do not exist. We developed an axenic method to grow C. campestris on an artificial host system (AHS). We evaluated the effects of nutrients and phytohormones on parasite haustoria development and growth. Haustorium morphology and gene expression were also characterized. The AHS consists of an inert, fibrous stick that mimics a host stem, wicking water and nutrients to the parasite. It enables C. campestris to exhibit a parasitic habit and develop through all stages of its life cycle, including production of new shoots and viable seeds. The phytohormones 1-naphthaleneacetic acid and 6-benzylaminopurine affect haustoria morphology and increase parasite fresh weight and biomass. Unigene expression in AHS haustoria reflects processes similar to those in haustoria on living host plants. The AHS is a methodological improvement for studying Cuscuta biology by avoiding specific host effects on the parasite and giving researchers full control of the parasite environment.
Salt stress alters membrane lipid content and lipid biosynthesis pathways in the plasma membrane and tonoplast
Authors: Guo Qi , Liu Lei , Rupasinghe Thusitha W T , Roessner Ute , Barkla Bronwyn J 
Published: March 2022

AbstractPlant cell membranes are the sites of sensing and initiation of rapid responses to changing environmental factors including salinity stress. Understanding the mechanisms involved in membrane remodeling is important for studying salt tolerance in plants. This task remains challenging in complex tissue due to suboptimal subcellular membrane isolation techniques. Here, we capitalized on the use of a surface charge-based separation method, free flow electrophoresis, to isolate the tonoplast (TP) and plasma membrane (PM) from leaf tissue of the halophyte ice plant (Mesembryanthemum crystallinum L.). Results demonstrated a membrane-specific lipidomic remodeling in this plant under salt conditions, including an increased proportion of bilayer forming lipid phosphatidylcholine in the TP and an increase in nonbilayer forming and negatively charged lipids (phosphatidylethanolamine and phosphatidylserine) in the PM. Quantitative proteomics showed salt-induced changes in proteins involved in fatty acid synthesis and desaturation, glycerolipid, and sterol synthesis, as well as proteins involved in lipid signaling, binding, and trafficking. These results reveal an essential plant mechanism for membrane homeostasis wherein lipidome remodeling in response to salt stress contributes to maintaining the physiological function of individual subcellular compartments.