bluuebunny/crossref_metadata_2025 huggingface dataset:
To bend without breaking: a qualitative study on leadership by doctors in Sierra Leone
Authors: Johnson Oliver , Sahr Foday , Begg Kerrin , Sevdalis Nick , Kelly Ann H
Published: June 2021

Strong leadership capabilities are essential for effective health services, yet definitions of leadership remain contested. Despite the acknowledged contextual specificity of leadership styles, most leadership theories draw heavily from Western conceptualizations. This cultural bias may attenuate the effectiveness of programmes intended to transform healthcare practice in Sub-Saharan Africa, where few empirical studies on health leadership have been conducted. This paper examines how effective leadership by doctors was perceived by stakeholders in one particular context, Sierra Leone. Drawing together extensive experience of in-country healthcare provision with a series of in-depth interviews with 27 Sierra Leonean doctors, we extended a grounded-theory approach to come to grips with the reach and relevance of contemporary leadership models in capturing the local experiences and relevance of leadership. We found that participants conceptualized leadership according to established leadership models, such as transformational and relational theories. However, participants also pointed to distinctive challenges attendant to healthcare provision in Sierra Leone that required specific leadership capabilities. Context-specific factors included health system breakdown, politicization in the health sector and lack of accountability, placing importance on skills such as persistence, role modelling and taking initiative. Participants also described pressure to behave in ways they deemed antithetical to their personal and professional values and also necessary in order to continue a career in the public sector. The challenge of navigating such ethical dilemmas was a defining feature of leadership in Sierra Leone. Our research demonstrates that while international leadership models were relevant in this context, there is strong emphasis on contingent or situational leadership theories. We further contribute to policy and practice by informing design of leadership development programmes and the establishment of a more enabling environment for medical leadership by governments and international donors.
Three decades of genetic privacy: a metaphoric journey
Authors: Knoppers Bartha Maria , Beauvais Michael J S
Published: June 2021

Debates surrounding genetic privacy have taken on different forms over the past 30 years. Taking genetic privacy to mean an interest that individuals, families, or even communities have with respect to genetic information, we examine the metaphors used in these debates to chronicle the development of genetic privacy. In 1990–2000, we examine claims for ownership and of ‘humanity’ spurred by the launch of the Human Genome Project and related endeavors. In 2000–2010, we analyze the interface of law and ethics with research infrastructures such as biobanks, for which notions of citizenship and ‘public goods’ were central. In 2010–2020, we detail the relational turn of genetic privacy in response of large international research consortia and big data. Although each decade had its leading conceptions of genetic privacy, the subject is neither strictly chronological nor static. We conclude with reflections on the nature of genetic privacy and the necessity to bring together the unique and private genetic self with the human other.
Pharmacokinetic-Pharmacodynamic Model of Vedolizumab for Targeting Endoscopic Remission in Patients With Crohn Disease: Posthoc Analysis of the LOVE-CD Study
Authors: Hanzel Jurij , Dreesen Erwin , Vermeire Séverine , Löwenberg Mark , Hoentjen Frank , Bossuyt Peter , Clasquin Esmé , Baert Filip J , D’Haens Geert R , Mathôt Ron
Published: June 2021

Background

Higher serum concentrations of vedolizumab have been associated with improved outcomes in inflammatory bowel disease. It is unclear how vedolizumab exposure is linked to endoscopic remission in Crohn disease (CD). We aimed to develop a pharmacokinetic-pharmacodynamic model linking vedolizumab exposure to endoscopic remission in CD.

Methods

Data were obtained from the first 110 patients participating in a phase 4 prospective multicenter trial (LOVE-CD; ClinicalTrials.gov identifier: NCT02646683), where vedolizumab was dosed at 300 mg every 8 weeks and serum concentrations and antibodies to vedolizumab were measured before each infusion. Concentration-time profiles were described by a 2-compartment model with parallel linear and nonlinear elimination. A first-order discrete-time Markov model was used to describe the relationship between pharmacokinetic exposure metrics and the probability of endoscopic remission (Simple Endoscopic Score for CD < 4).

Results

Linear clearance was 0.215 L/d, and the volume of distribution of the central compartment was 4.92 L. Linear clearance was higher and vedolizumab exposure was lower in patients with lower serum albumin concentrations, in the presence of antibodies to vedolizumab, and in patients with previous exposure to other biologic therapy. A week 22 vedolizumab concentration of 20.0 mg/L was predicted to yield a 35% probability of achieving endoscopic remission at week 26. Model-based simulations suggested that endoscopic remission rates of 46.5% or 40.0% could be reached with every-4-weeks dosing in patients who were naïve or previously exposed to biologic therapy, respectively.

Conclusions

Model-informed dosing of vedolizumab in CD provides a foundation for future research aiming to maximize endoscopic remission rates.
Posttraumatic Stress in Patients With Inflammatory Bowel Disease: Prevalence and Relationships to Patient-Reported Outcomes
Authors: Taft Tiffany H , Quinton Sarah , Jedel Sharon , Simons Madison , Mutlu Ece A , Hanauer Stephen B
Published: June 2021

Background

Patients with chronic illness are at increased risk for traumatic stress because of medical trauma. Initial studies of posttraumatic stress (PTS) in patients with inflammatory bowel disease (IBD) have found that approximately one-third of patients may experience significant PTS symptoms including flashbacks, nightmares, hypervigilance, disrupted sleep, and low mood. We aim to better characterize PTS in IBD and its relationship with patient outcomes in a large cohort of patients with IBD.

Methods

Adult patients registered with the Crohn’s & Colitis Foundation/University of North Carolina IBD Partners database were invited to complete a supplementary survey between February and July 2020. The Post Traumatic Stress Disorder Checklist-5th edition was administered as a supplemental survey. Additional data from IBD Partners included disease severity, surgery and hospital history, demographics, and health care utilization.

Results

A total of 797 patients participated (452 with Crohn disease, 345 with ulcerative colitis). No impacts on response patterns because of the COVID-19 pandemic were found. Although 5.6% of the sample reported an existing PTS diagnosis because of IBD experiences, 9.6% of participants met the full IBD-related PTS diagnostic criteria per the Post Traumatic Stress Disorder Checklist-5th edition. Female patients, younger patients, those with less educational attainment, non-White patients, and Hispanic patients reported higher levels of PTS symptoms. Patients with higher PTS symptoms were more likely to have been hospitalized, have had surgery, have more severe symptoms, and not be in remission. Increased PTS was also associated with increased anxiety, depression, pain interference, fatigue, and health care utilization.

Conclusions

The present findings support prior research that approximately one-quarter to one-third of patients with IBD report significant symptoms of PTS directly from their disease experiences, and certain demographic groups are at higher risk. In addition, PTS is associated with several IBD outcomes. Patients with higher PTS symptoms are less likely to be in remission and may utilize more outpatient gastrointestinal services. Intervention trials to mitigate PTS symptoms in patients with IBD are warranted.
The effects of spatiotemporal scale on commercial fishery abundance index suitability
Authors: Wang Jintao , Boenish Robert , Chen Xinjun , Tian Siquan , Zhu JiangFeng
Published: June 2021

With consideration of sophisticated modern commercial fisheries, the commonly used metric catch per unit effort (CPUE) may not be a reasonable proxy for generating abundance indices (AIs) for all species. Presumably, spatiotemporal scale is a critical factor that affects the accuracy of local/aggregated AIs derived from spatial modelling approaches, thus it is necessary to evaluate how scale affects scientific estimates of abundance. We explored three commonly utilized AI proxies, including aggregated catch (CatchAI), aggregated effort (EffortAI), and CPUEAI from the perspective of accuracy and spatial representational ability using a neural network (NN) model at different spatiotemporal scales. As a case example, we grouped the Chinese fleet's Northwest Pacific neon flying squid (Ommastrephes bartramii) fishery dataset (2009–2018) at four spatial scales (0.25° × 0.25°, 0.5° × 0.5°, 1° × 1°, 2° × 2°) to construct monthly and annual resolution models. The results showed that for both simulated and real datasets, AIs based on catch data had better accuracy, consistency, and spatial representational ability compared to CPUE and effort-dependent AI models at all spatial scales. Relative to the finest spatial scale, only results from the model with 0.5° × 0.5° resolution preserved enough distributional detail to reflect the known migration route for O. bartramii. Model results exhibited large variation dependent on spatial scale, particularly amongst CPUEAI scenarios. We suggest that scale comparisons among potential proxies should be conducted prior to AIs being used for applications such as population trends in stock assessment.
On the convergence and mesh-independent property of the Barzilai–Borwein method for PDE-constrained optimization
Authors: Azmi Behzad , Kunisch Karl
Published: June 2021

Aiming at optimization problems governed by partial differential equations (PDEs), local R-linear convergence of the Barzilai–Borwein (BB) method for a class of twice continuously Fréchet-differentiable functions is proven. Relying on this result, the mesh-independent principle for the BB-method is investigated. The applicability of the theoretical results is demonstrated for two different types of PDE-constrained optimization problems. Numerical experiments are given, which illustrate the theoretical results.
Notch signaling supports the appearance of follicular helper T cells in the Peyer’s patches concomitantly with the reduction of regulatory T cells
Authors: Yazawa Masaki , Hosokawa Hiroyuki , Koizumi Maria , Hirano Ken-ichi , Imai Jin , Hozumi Katsuto
Published: June 2021

The intracellular fragment of Notch1, a mediator of Notch signaling that is frequently detected in thymic immigrants, is critical for specifying T-cell fate in the thymus, where Delta-like 4 (Dll4) functions as a Notch ligand on the epithelium. However, as such Notch signaling has not been detected in mature T cells, how Notch signaling contributes to their response in secondary lymphoid organs has not yet been fully defined. Here, we detected the marked expression of Dll4 on the stromal cells and the active fragment of Notch1 (Notch1 intracellular domain, N1ICD) in CD4+ T cells in the follicles of Peyer’s patches (PPs). In addition, N1ICD-bearing T cells were found in the T-cell zone of PPs, especially in the transcription factor Foxp3+ regulatory T (Treg) cells, with slight expression of Dll4 on the stromal cells. These fragments disappeared in Dll4-deficient conditions. It was also found that Notch1- and Notch2-deficient T cells preferentially differentiated into Treg cells in PPs, but not CXCR5+PD-1+ follicular helper T (Tfh) cells. Moreover, these phenotypes were also observed in chimeric mice reconstituted with the control and T-cell-specific Notch1/2-deficient bone marrow or Treg cells. These results demonstrated that Dll4-mediated Notch signaling in PPs is required for the efficient appearance of Tfh cells in a Treg cell-prone environment, which is common among the gut-associated lymphoid tissues, and is critical for the generation of Tfh-mediated germinal center B cells.
Military Experience and Elite Decision-Making: Self-Selection, Socialization, and the Vietnam Draft Lottery
Authors: Lupton Danielle L
Published: June 2021

Scholars across international relations (IR) debate the role military experience plays in elite decision-making. I argue there are two critical problems with this debate. First, it fails to adequately consider the underlying mechanisms linking military service to elite policy preferences. Second, it narrowly focuses on the use of force and largely ignores other ways in which military experience may shape elite behavior. I employ vulnerability to the Vietnam draft lottery to disentangle the impact of two key mechanisms linking military service to elite preferences: self-selection and socialization. I compare the foreign and defense policy roll call votes of Members of Congress (MCs) in the House of Representatives across the 94th–113th Congresses who were eligible for the draft and served in the military to those who were eligible for the draft but did not serve. I find significant differences in the roll call voting behavior between these groups, particularly on issues associated with arming and defense budget restrictions, as well as broader oversight of the military. These effects are heightened for MCs who served on active duty, in the military longer, and in combat, providing strong support for socialization effects. My study carries implications for civil–military relations, elite decision-making, and the study of leaders in IR.
Mechanisms of antibiotic resistance of Clostridioides difficile
Authors: Wickramage Ishani , Spigaglia Patrizia , Sun Xingmin
Published: June 2021

Clostridioides difficile (CD) is one of the top five urgent antibiotic resistance threats in USA. There is a worldwide increase in MDR of CD, with emergence of novel strains which are often more virulent and MDR. Antibiotic resistance in CD is constantly evolving with acquisition of novel resistance mechanisms, which can be transferred between different species of bacteria and among different CD strains present in the clinical setting, community, and environment. Therefore, understanding the antibiotic resistance mechanisms of CD is important to guide optimal antibiotic stewardship policies and to identify novel therapeutic targets to combat CD as well as other bacteria. Epidemiology of CD is driven by the evolution of antibiotic resistance. Prevalence of different CD strains and their characteristic resistomes show distinct global geographical patterns. Understanding epidemiologically driven and strain-specific characteristics of antibiotic resistance is important for effective epidemiological surveillance of antibiotic resistance and to curb the inter-strain and -species spread of the CD resistome. CD has developed resistance to antibiotics with diverse mechanisms such as drug alteration, modification of the antibiotic target site and extrusion of drugs via efflux pumps. In this review, we summarized the most recent advancements in the understanding of mechanisms of antibiotic resistance in CD and analysed the antibiotic resistance factors present in genomes of a few representative well known, epidemic and MDR CD strains found predominantly in different regions of the world.
Interpretable disease prediction using heterogeneous patient records with self-attentive fusion encoder
Authors: Kwak Heeyoung , Chang Jooyoung , Choe Byeongjin , Park Sangmin , Jung Kyomin
Published: June 2021

Objective

We propose an interpretable disease prediction model that efficiently fuses multiple types of patient records using a self-attentive fusion encoder. We assessed the model performance in predicting cardiovascular disease events, given the records of a general patient population.

Materials and Methods

We extracted 798111 ses and 67 623 controls from the sample cohort database and nationwide healthcare claims data of South Korea. Among the information provided, our model used the sequential records of medical codes and patient characteristics, such as demographic profiles and the most recent health examination results. These two types of patient records were combined in our self-attentive fusion module, whereas previously dominant methods aggregated them using a simple concatenation. The prediction performance was compared to state-of-the-art recurrent neural network-based approaches and other widely used machine learning approaches.

Results

Our model outperformed all the other compared methods in predicting cardiovascular disease events. It achieved an area under the curve of 0.839, while the other compared methods achieved between 0.74111 d 0.830. Moreover, our model consistently outperformed the other methods in a more challenging setting in which we tested the model’s ability to draw an inference from more nonobvious, diverse factors.

Discussion

We also interpreted the attention weights provided by our model as the relative importance of each time step in the sequence. We showed that our model reveals the informative parts of the patients’ history by measuring the attention weights.

Conclusion

We suggest an interpretable disease prediction model that efficiently fuses heterogeneous patient records and demonstrates superior disease prediction performance.
Isotope analysis reveals dietary overlap among sympatric canids
Authors: Webster Sarah C , Chamberlain Michael J , Hinton Joseph W , Beasley James C
Published: June 2021

When colonizing new regions, invading species might compete strongly with phylogenetically related species native to the regions they are colonizing, eventually leading to coexistence or displacement. In the southeast of the United States, recently established coyotes (Canis latrans) compete with red fox (Vulpes vulpes) and gray fox (Urocyon cinereoargenteus), although it remains unclear if competition is leading to resource partitioning or displacement by species. Using nitrogen and carbon stable isotopes, we tested the hypothesis that coyotes compete with foxes for food resources, with canids partitioning those resources to mitigate competition. We compared diets of canids in the southeast to those in the Plains region of the United States, a region where all three species historically have coexisted. We analyzed 217 hair samples from both regions pre-1960, prior to coyote colonization of the southeast, and post-2000, after coyotes were ubiquitous there, to assess differences in diet among species for both regions (southeast versus Plains and time periods, pre- versus postcolonization by coyotes). Modeling revealed significant dietary overlap among historical and contemporary populations in the southeast. Historically, all species partitioned resources in the Plains. Contemporarily, red fox and coyotes co-occurring in the Plains overlapped in diet; however, gray fox diet did not overlap with those of red fox and coyotes. Absence of partitioning in diet among co-occurring canids in the southeast indicates that interspecific competition could be strong in the region. Competition among canid populations in the southeast could lead to further resource partitioning among species that promotes coexistence or competitive exclusion of smaller fox species where coyote populations are abundant.
Association of the COVID-19 Pandemic With Patterns of Statewide Cancer Services
Authors: Yabroff K Robin , Wu Xiao-Cheng , Negoita Serban , Stevens Jennifer , Coyle Linda , Zhao Jingxuan , Mumphrey Brent J , Jemal Ahmedin , Ward Kevin C
Published: June 2021

The coronavirus disease 2019 (COVID-19) pandemic led to delayed medical care in the United States. We examined changes in patterns of cancer diagnosis and surgical treatment between January 1 and December 31 in 2020 and 2019 with real-time electronic pathology report data from population-based Surveillance, Epidemiology, and End Results cancer registries from Georgia and Louisiana. During 2020, there were 29 905 fewer pathology reports than in 2019, representing a 10.2% decline. Declines were observed in all age groups, including children and adolescents younger than 18 years. The nadir was early April 2020, with 42.8% fewer reports than in April 2019. Numbers of reports through December 2020 never consistently exceeded those in 2019 after first declines. Patterns were similar by age group and cancer site. Findings suggest substantial delays in diagnosis and treatment services for cancers during the pandemic. Ongoing evaluation can inform public health efforts to minimize any lasting adverse effects of the pandemic on cancer diagnosis, stage, treatment, and survival.
Nondiscrimination in Standard Essential Patents; ND Prong V. Art. 102(C) TFEU
Authors: Botta Marco
Published: June 2021

The article analyses the meaning of the nondiscriminatory principle in disputes concerning Standard Essential Patents (SEPs) under EU competition and contract law (that is, ND prong). The article reviews the economics literature, looking at the welfare effect of price discrimination and the interpretation of the ND prong provided by a number of economists. Secondly, the article analyses the case law of the EU Court of Justice on Art. 102(c) TFEU and recent rulings by the German and British courts concerning the scope of the application of the ND prong. A strategy of discrimination in regard to royalty rates may be sanctioned, both under competition and contract law. However, Art. 102(c) requires a higher burden of proof than contract law. As a consequence, it is unsurprising that no case of royalty rate discrimination has ever been sanctioned in Europe as an abuse of dominance. While courts and economists generally agree that the ND prong is applicable only when licensees are “similarly situated,” to date, there is no common understanding of the meaning of this expression. In particular, it is unclear whether, and to what extent, licensees are “similarly situated” if they are not competitors in the downstream market.
Can Understory Plant Composition and Richness Help Designate Riparian Management Zones in Mesic Headwater Forests of the Northeastern United States?
Authors: Jayasuriya Maneesha T , Stella John C , Germain René H
Published: June 2021

Riparian buffers implemented to minimize sediment, nutrients, and disturbance impacts on streams during forest operations vary greatly in the degree to which ecological criteria are used in their design. Because most forest operations are concentrated around headwater streams, our primary research objective was to identify a floristically based riparian boundary for headwater streams using plant species composition and indicator species to classify riparian environments distinct from the surrounding upland forest. Within three forested regions of the Northeast US, understory vegetation plots were sampled along perpendicular transects extending from the stream bank into the upland forest. At all sites, species richness was highest adjacent to the stream, decreasing exponentially within 6–12 m from the channel. Species composition closest to the stream was significantly different from all other lateral distances, but identified riparian indicator species were of limited practical use across all sites. However, changes in species richness can serve to identify a riparian area extent up to 6–12 m from headwater streams.
The Statewide Economic Impact of Child Care–Associated Viral Acute Gastroenteritis Infections
Authors: Hayashi Michael A L , Eisenberg Joseph N S , Martin Emily T , Hashikawa Andrew N
Published: June 2021

Introduction

More than 65% of children aged ≤5 years in the United States require out-of-home child care. Child care attendance has been associated with an elevated risk of respiratory illness and acute gastroenteritis (AGE). While child care–associated respiratory disease cases are more numerous, AGE is associated with more severe symptoms and more than double the number of absences from child care. In addition, viral pathogens such as norovirus, rotavirus, and adenovirus are highly infectious and may be spread to parents and other household members. As a result, child care–associated viral AGE may incur substantial economic costs due to healthcare service usage and lost productivity.

Methods

We used surveillance data from a network of child care centers in Washtenaw County, Michigan, as well as a household transmission model to estimate the annual cost of child care–associated viral AGE in the state of Michigan.

Results

We estimated that child care–associated viral AGE in Michigan costs between $15 million and $31 million annually, primarily due to lost productivity.

Conclusions

The economic burden of child care–associated infections is considerable. Effective targeted interventions are needed to mitigate this impact.
Evaluation of the effects of nanoparticles on the therapeutic function of platelet: a review
Authors: Zadeh Mehrizi Tahereh , Amini Kafiabad Sedigheh
Published: June 2021

Objectives

Nanotechnology and nanoparticles are used in different applications in disease monitoring and therapy in contact with blood. Nanoparticles showed different effects on blood components and reduced or improved the function of therapeutic platelet during the storage time. This review study was performed to evaluate the impacts of various sizes and charges of nanoparticles on platelet function and storage time. The present review contains the literature between 2010 and 2020. The data have been used from different sites such as PubMed, Wiley, ScienceDirect and online electronic journals.

Key findings

From the literature survey, it has been demonstrated that among various properties, size and charge of nanoparticles were critical on the function of therapeutic platelet during the storage and inhibition of their aggregation. Overall, this study described that nanoparticles with smaller size and negative charge were more effective in increasing the survival time, inhibition of aggregation and improving the function of therapeutic platelet.

Based on the current review, it can be confirmed that nanoparticles such as dendrimer, Au, Ag and iron oxide nanoparticles with smaller size and negative charge have significant advantages for improving the efficacy of platelets during the storage chain and inhibition of their aggregation.
Surgical repair of a right coronary aneurysm with a coronary artery fistula to the right atrium
Authors: Yokoyama Shigeki , Nagao Kanetsugu , Higashida Akihiko , Aoki Masaya , Yamashita Shigeyuki , Yamashita Akio , Doi Toshio , Fukahara Kazuaki , Yoshimura Naoki
Published: June 2021

A coronary artery fistula is a rare condition caused by abnormal coronary artery embryological development. Although most cases are asymptomatic, in some, the large shunt volume and the myocardial ischemia due to the steal phenomenon require surgical treatment. We present the case of a 40-year-old woman who presented with angina on exertion. Enhanced computed tomography showed a giant right coronary artery (RCA) aneurysm with an RCA-to-right atrium fistula. Because of the presence of symptoms and the presence of large fistulous tract, the patient was considered a surgical candidate. The procedure was performed under cardiopulmonary bypass. Ligation and closure of the fistula were performed in combination with dissection of the enlarged main trunk of the RCA and coronary artery bypass using the internal thoracic artery because of its potential for long-term patency. The postoperative course was uneventful.
A high concentration of abscisic acid inhibits hypocotyl phototropism in Gossypium arboreum by reducing accumulation and asymmetric distribution of auxin
Authors: Zhu Jin-Dong , Wang Jing , Guo Xi-Ning , Shang Bao-Shuan , Yan Hong-Ru , Zhang Xiao , Zhao Xiang
Published: June 2021

Hypocotyl phototropism is mediated by the phototropins and plays a critical role in seedling morphogenesis by optimizing growth orientation. However, the mechanisms by which phototropism influences morphogenesis require additional study, especially for polyploid crops such as cotton. Here, we found that hypocotyl phototropism was weaker in Gossypium arboreum than in G. raimondii (two diploid cotton species), and LC-MS analysis indicated that G. arboreum hypocotyls had a higher content of abscisic acid (ABA) and a lower content of indole-3-acetic acid (IAA) and bioactive gibberellins (GAs). Consistently, the expression of ABA2, AAO3, and GA2OX1 was higher in G. arboreum than in G. raimondii, and that of GA3OX was lower; these changes promoted ABA synthesis and the transformation of active GA to inactive GA. Higher concentrations of ABA inhibited the asymmetric distribution of IAA across the hypocotyl and blocked the phototropic curvature of G. raimondii. Application of IAA or GA3 to the shaded and illuminated sides of the hypocotyl enhanced and inhibited phototropic curvature, respectively, in G. arboreum. The application of IAA, but not GA, to one side of the hypocotyl caused hypocotyl curvature in the dark. These results indicate that the asymmetric distribution of IAA promotes phototropic growth, and the weakened phototropic curvature of G. arboreum may be attributed to its higher ABA concentrations that inhibit the action of auxin, which is regulated by GA signaling.
3D MHD simulations of accretion on to stars with tilted magnetic and rotational axes
Authors: Romanova M M , Koldoba A V , Ustyugova G V , Blinova A A , Lai D , Lovelace R V E
Published: June 2021

We present results of global 3D magnetohydrodynamic simulations of accretion on to magnetized stars where both the magnetic and rotational axes of the star are tilted about the rotational axis of the disc. We observed that initially the inner parts of the disc are warped, tilted, and precess due to the magnetic interaction between the magnetosphere and the disc. Later, larger tilted discs form with the size increasing with the magnetic moment of the star. The normal vector to the discs are tilted at different angles, from ∼5°–10° up to ∼30°–40°. Small tilts may result from the winding of the magnetic field lines about the rotational axis of the star and the action of the magnetic force which tends to align the disc. Another possible explanation is the magnetic Bardeen–Petterson effect in which the disc settles in the equatorial plane of the star due to precessional and viscous torques in the disc. Tilted discs slowly precess with the time-scale of the order of ∼50 Keplerian periods at the reference radius (∼3 stellar radii). Our results can be applied to different types of stars where signs of tilted discs and/or slow precession have been observed.
The onset of gravothermal core collapse in velocity-dependent self-interacting dark matter subhaloes
Authors: Turner Hannah C , Lovell Mark R , Zavala Jesús , Vogelsberger Mark
Published: June 2021

It has been proposed that gravothermal collapse due to dark matter self-interactions (i.e. self-interacting dark matter, SIDM) can explain the observed diversity of the Milky Way (MW) satellites’ central dynamical masses. We investigate the process behind this hypothesis using an N-body simulation of a MW-analogue halo with velocity-dependent SIDM (vdSIDM) in which the low-velocity self-scattering cross-section, $\sigma _{\rm T}/m_{\rm x}$, reaches 100 cm2 g−1; we dub this model the vd100 model. We compare the results of this simulation to simulations of the same halo that employ different dark models, including cold dark matter (CDM) and other, less extreme SIDM models. The masses of the vd100 haloes are very similar to their CDM counterparts, but the values of their maximum circular velocities, Vmax, are significantly higher. We determine that these high Vmax subhaloes were objects in the mass range [5 × 106, 1 × 108] M⊙ at z = 1 that undergo gravothermal core collapse. These collapsed haloes have density profiles that are described by single power laws down to the resolution limit of the simulation, and the inner slope of this density profile is approximately −3. Resolving the ever decreasing collapsed region is challenging, and tailored simulations will be required to model the runaway instability accurately at scales <1 kpc.
An MHD spectral theory approach to Jeans’ magnetized gravitational instability
Authors: Durrive Jean-Baptiste , Keppens Rony , Langer Mathieu
Published: June 2021

In this paper, we revisit the governing equations for linear magnetohydrodynamic (MHD) waves and instabilities existing within a magnetized, plane-parallel, self-gravitating slab. Our approach allows for fully non-uniformly magnetized slabs, which deviate from isothermal conditions, such that the well-known Alfvén and slow continuous spectra enter the description. We generalize modern MHD textbook treatments, by showing how self-gravity enters the MHD wave equation, beyond the frequently adopted Cowling approximation. This clarifies how Jeans’ instability generalizes from hydro to MHD conditions without assuming the usual Jeans’ swindle approach. Our main contribution lies in reformulating the completely general governing wave equations in a number of mathematically equivalent forms, ranging from a coupled Sturm–Liouville formulation, to a Hamiltonian formulation linked to coupled harmonic oscillators, up to a convenient matrix differential form. The latter allows us to derive analytically the eigenfunctions of a magnetized, self-gravitating thin slab. In addition, as an example, we give the exact closed form dispersion relations for the hydrodynamical p- and Jeans-unstable modes, with the latter demonstrating how the Cowling approximation modifies due to a proper treatment of self-gravity. The various reformulations of the MHD wave equation open up new avenues for future MHD spectral studies of instabilities as relevant for cosmic filament formation, which can e.g. use modern formal solution strategies tailored to solve coupled Sturm–Liouville or harmonic oscillator problems.
mg-mamposst: a code to test modifications of gravity with internal kinematics and lensing analyses of galaxy clusters
Authors: Pizzuti Lorenzo , Saltas Ippocratis D , Amendola Luca
Published: June 2021

We present an upgraded version of mg-mamposst, an extension of the mamposst (Modelling Anisotropy and Mass Profile of Spherical Observed Systems) algorithm that performs Bayesian fits of models of mass and velocity anisotropy profiles to the distribution of tracers in projected phase space, to handle modified gravity models and constrain their parameters. The new version implements two distinct types of gravity modifications, namely general chameleon and Vainshtein screening, and is further equipped with a Monte Carlo Markov chain module for an efficient parameter space exploration. The programme is complemented by the clustergen code, capable of producing mock galaxy clusters under the assumption of spherical symmetry, dynamical equilibrium, and Gaussian local velocity distribution functions as in mamposst. We demonstrate the potential of the method by analysing a set of synthetic, isolated spherically symmetric dark matter haloes, focusing on the statistical degeneracies between model parameters. Assuming the availability of additional lensing-like information, we forecast the constraints on the modified gravity parameters for the two models presented, as expected from joint lensing + internal kinematics analyses, in view of upcoming galaxy cluster surveys. In Vainshtein screening, we forecast the weak lensing effect through the estimation of the full convergence-shear profile. For chameleon screening, we constrain the allowed region in the space of the two free parameters of the model, further focusing on the $\displaystyle f(\mathcal {R})$ subclass to obtain realistic bounds on the background field $\displaystyle |f_{\mathcal {R}0}|$. Our analysis demonstrates the complementarity of internal kinematics and lensing probes for constraining modified gravity theories, and how the bounds on Vainshtein-screened theories improve through the combination of the two probes.
Instability analysis for spiral arms of local galaxies: M51, NGC 3627, and NGC 628
Authors: Inoue Shigeki , Takagi Toshinobu , Miyazaki Atsushi , Cooper Erin Mentuch , Egusa Fumi , Yajima Hidenobu
Published: June 2021

We investigate dynamical states of grand-design spiral arms in three local galaxies: M51, NGC 3627, and NGC 628. Based on linear perturbation analysis considering multiple components in the galaxies, we compute instability parameters of the spiral arms using their observational data and argue whether the arms will fragment by their self-gravity. Our analysis utilizes observations of carbon monoxide (CO), 21-cm line emission, and multiband photometric images for molecular gas, atomic gas, and stellar components in the arms, respectively. We find that the grand-design arms of these galaxies indicate marginally stable states, and hence they are not on the way to fragment. We consider this to be consistent with the commonness of spiral galaxies and the relative rarity of fragmented discs at low redshifts. In the analysis, molecular gas is the dominant component to determine the (in)stability of the arms, whereas atomic gas and stars are far less important. Therefore, the results of our analysis are sensitive to an assumed CO-to-H2 conversion factor. If we assume a typical scatter of the measurements and admit nearly twice as large a conversion factor as our fiducial value, our analysis results in predicting the instability for the spiral arms. More sophisticated determination of the conversion factor is required for more accurate analysis for the (in)stability of spiral arms.
The formation of barium giants via mass accretion in binary systems
Authors: Stancliffe Richard J
Published: June 2021

We examine the composition of barium stars in the context of mass transfer from an asymptotic giant branch (AGB) companion. We accrete between 0.01 and 0.5 M⊙ of AGB ejecta on to low-mass companions of [Fe/H]  = −0.25 at the ages expected for the end of the lives of AGB stars of 2.5, 3, and 4 M⊙. In each case, we form a star of 2.5 M⊙ that is thought to be a typical barium star mass. We discuss the extent of dilution of accreted material as the star evolves, and describe the impact on the surface abundances. For accretion from a 2.5 M⊙ primary, if the secondary’s initial mass is 2.45 M⊙ or more, accretion takes place when the secondary is undergoing core helium burning. Using data from the sample of De Castro et al., we attempt to fit the observed properties of 74 barium giants using the models we have computed. We find that all but six of these objects are best fit using ejecta from 2.5 M⊙ (32 objects) or 3 M⊙ (36 objects) AGB stars. Higher accretion masses are typically required when accreting from a lower mass companion. We find accretion masses that are broadly consistent with recent hydrodynamical simulations of wind mass transfer, though the accretion efficiency is towards the upper limit found in these simulations. For the 18 stars with reported orbital periods, we find no strong correlations between period and accretion mass.
Exploring the spectral properties of radio relics – I: integrated spectral index and Mach number
Authors: Wittor D , Ettori S , Vazza F , Rajpurohit K , Hoeft M , Domínguez-Fernández P
Published: June 2021

Radio relics are the manifestation of electrons presumably being shock (re-)accelerated to high energies in the outskirts of galaxy clusters. However, estimates of the shocks’ strength yield different results when measured with radio or X-ray observations. In general, Mach numbers obtained from radio observations are larger than the corresponding X-ray measurements. In this work, we investigate this Mach number discrepancy. For this purpose, we used the cosmological code enzo to simulate a sample of galaxy clusters that host bright radio relics. For each relic, we computed the radio Mach number from the integrated radio spectrum and the X-ray Mach number from the X-ray surface brightness and temperature jumps. Our analysis suggests that the differences in the Mach number estimates follow from the way in which different observables are related to different parts of the underlying Mach number distribution: radio observations are more sensistive to the high Mach numbers present only in a small fraction of a shock’s surface, while X-ray measurements reflect the average of the Mach number distribution. Moreover, X-ray measurements are very sensitive to the relic’s orientation. If the same relic is observed from different sides, the measured X-ray Mach number varies significantly. On the other hand, the radio measurements are more robust, as they are unaffected by the relic’s orientation.
Light, medium-weight, or heavy? The nature of the first supermassive black hole seeds
Authors: Sassano Federica , Schneider Raffaella , Valiante Rosa , Inayoshi Kohei , Chon Sunmyon , Omukai Kazuyuki , Mayer Lucio , Capelo Pedro R
Published: June 2021

Observations of hyper-luminous quasars at z>6 reveal the rapid growth of supermassive black holes (SMBHs ${\gt}10^9 \,\rm M_{\odot }$) whose origin is still difficult to explain. Their progenitors may have formed as remnants of massive, metal-free stars (light seeds), via stellar collisions (medium-weight seeds) and/or massive gas clouds direct collapse (heavy seeds). In this work, we investigate for the first time the relative role of these three seed populations in the formation of z>6 SMBHs within an Eddington-limited gas accretion scenario. To this aim, we implement in our semi-analytical data-constrained model a statistical description of the spatial fluctuations of Lyman–Werner (LW) photodissociating radiation and of metal/dust enrichment. This allows us to set the physical conditions for black hole seeds formation, exploring their relative birth rate in a highly biased region of the Universe at z>6. We find that the inclusion of medium-weight seeds does not qualitatively change the growth history of the first SMBHs: although less massive seeds (${\lt}10^3\, \rm M_\odot$) form at a higher rate, the mass growth of a ${\sim}10^9\, \rm M_\odot$ SMBH at z<15 is driven by efficient gas accretion (at a sub-Eddington rate) on to its heavy progenitors ($10^5\, \rm M_\odot$). This conclusion holds independently of the critical level of LW radiation and even when medium-weight seeds are allowed to form in higher metallicity galaxies, via the so-called supercompetitive accretion scenario. Our study suggests that the genealogy of z∼6 SMBHs is characterized by a rich variety of BH progenitors, which represent only a small fraction (${\lt} 10{-}20{{\ \rm per\ cent}}$) of all the BHs that seed galaxies at z>15.
A Spitzer survey for dust-obscured supernovae
Authors: Fox Ori D , Khandrika Harish , Rubin David , Casper Chadwick , Li Gary Z , Szalai Tamás , Armus Lee , Filippenko Alexei V , Skrutskie Michael F , Strolger Lou , Van Dyk Schuyler D
Published: June 2021

Supernova (SN) rates serve as an important probe of star formation models and initial mass functions. Near-infrared seeing-limited ground-based surveys typically discover a factor of 3–10 fewer SNe than predicted from far-infrared luminosities owing to sensitivity limitations arising from both a variable point-spread function (PSF) and high dust extinction in the nuclear regions of star-forming galaxies. This inconsistency has potential implications for our understanding of star-formation rates and massive-star evolution, particularly at higher redshifts, where star-forming galaxies are more common. To resolve this inconsistency, a successful SN survey in the local universe must be conducted at longer wavelengths and with a space-based telescope, which has a stable PSF to reduce the necessity for any subtraction algorithms and thus residuals. Here, we report on a 2-yr Spitzer/IRAC 3.6 $\mu$m survey for dust-extinguished SNe in the nuclear regions of forty luminous infrared galaxies (LIRGs) within 200 Mpc. The asymmetric Spitzer PSF results in worse than expected subtraction residuals when implementing standard template subtraction. Forward-modelling techniques improve our sensitivity by several ∼1.5 mag. We report the detection of 9 SNe, five of which were not discovered by optical surveys. After adjusting our predicted rates to account for the sensitivity of our survey, we find that the number of detections is consistent with the models. While this search is none the less hampered by a difficult-to-model PSF and the relatively poor resolution of Spitzer, it will benefit from future missions, such as Roman and the James Webb Space Telescope, with higher resolution and more symmetric PSFs.
Extending the evolution of the stellar mass–size relation at z ≤ 2 to low stellar mass galaxies from HFF and CANDELS
Authors: Nedkova Kalina V , Häußler Boris , Marchesini Danilo , Dimauro Paola , Brammer Gabriel , Eigenthaler Paul , Feinstein Adina D , Ferguson Henry C , Huertas-Company Marc , Johnston Evelyn J , Kado-Fong Erin , Kartaltepe Jeyhan S , Labbé Ivo , Lange-Vagle Daniel , Martis Nicholas S , McGrath Elizabeth J , Muzzin Adam , Oesch Pascal , Ordenes-Briceño Yasna , Puzia Thomas , Shipley Heath V , Simmons Brooke D , Skelton Rosalind E , Stefanon Mauro , van der Wel Arjen , Whitaker Katherine E
Published: June 2021

We reliably extend the stellar mass–size relation over 0.2 ≤ z ≤ 2 to low stellar mass galaxies by combining the depth of Hubble Frontier Fields with the large volume covered by CANDELS. Galaxies are simultaneously modelled in multiple bands using the tools developed by the MegaMorph project, allowing robust size (i.e. half-light radius) estimates even for small, faint, and high redshift galaxies. We show that above 107 M⊙, star-forming galaxies are well represented by a single power law on the mass–size plane over our entire redshift range. Conversely, the stellar mass–size relation is steep for quiescent galaxies with stellar masses $\ge 10^{10.3}\, {\rm M}_\odot$ and flattens at lower masses, regardless of whether quiescence is selected based on star-formation activity, rest-frame colours, or structural characteristics. This flattening occurs at sizes of ∼1 kpc at z ≤ 1. As a result, a double power law is preferred for the stellar mass–size relation of quiescent galaxies, at least above 10$^7\, {\rm M}_\odot$. We find no strong redshift dependence in the slope of the relation of star-forming galaxies as well as of high mass quiescent galaxies. We also show that star-forming galaxies with stellar masses $\ge 10^{9.5}\, {\rm M}_\odot$ and quiescent galaxies with stellar masses $\ge 10^{10.3}\, {\rm M}_\odot$ have undergone significant size growth since z ∼ 2, as expected; however, low mass galaxies have not. Finally, we supplement our data with predominantly quiescent dwarf galaxies from the core of the Fornax cluster, showing that the stellar mass–size relation is continuous below 10$^7\, {\rm M}_\odot$, but a more complicated functional form is necessary to describe the relation.