233 research outputs found
Gravitating discs around black holes
Fluid discs and tori around black holes are discussed within different
approaches and with the emphasis on the role of disc gravity. First reviewed
are the prospects of investigating the gravitational field of a black
hole--disc system by analytical solutions of stationary, axially symmetric
Einstein's equations. Then, more detailed considerations are focused to middle
and outer parts of extended disc-like configurations where relativistic effects
are small and the Newtonian description is adequate.
Within general relativity, only a static case has been analysed in detail.
Results are often very inspiring, however, simplifying assumptions must be
imposed: ad hoc profiles of the disc density are commonly assumed and the
effects of frame-dragging and completely lacking. Astrophysical discs (e.g.
accretion discs in active galactic nuclei) typically extend far beyond the
relativistic domain and are fairly diluted. However, self-gravity is still
essential for their structure and evolution, as well as for their radiation
emission and the impact on the environment around. For example, a nuclear star
cluster in a galactic centre may bear various imprints of mutual star--disc
interactions, which can be recognised in observational properties, such as the
relation between the central mass and stellar velocity dispersion.Comment: Accepted for publication in CQG; high-resolution figures will be
available from http://www.iop.org/EJ/journal/CQ
SN2023ixf in Messier 101: the twilight years of the progenitor as seen by Pan-STARRS
The nearby type II supernova, SN2023ixf in M101 exhibits signatures of
early-time interaction with circumstellar material in the first week
post-explosion. This material may be the consequence of prior mass loss
suffered by the progenitor which possibly manifested in the form of a
detectable pre-supernova outburst. We present an analysis of the long-baseline
pre-explosion photometric data in , , , , and filters from
Pan-STARRS as part of the Young Supernova Experiment, spanning 5,000
days. We find no significant detections in the Pan-STARRS pre-explosion light
curve. We train a multilayer perceptron neural network to classify
pre-supernova outbursts. We find no evidence of eruptive pre-supernova activity
to a limiting absolute magnitude of . The limiting magnitudes from the full
set of (average absolute magnitude -8) data are consistent
with previous pre-explosion studies. We use deep photometry from the literature
to constrain the progenitor of SN2023ixf, finding that these data are
consistent with a dusty red supergiant (RSG) progenitor with luminosity
5.12 and temperature 3950K,
corresponding to a mass of 14-20 MComment: 19 pages, 8 figures, 1 tabl
Early Clinical Manifestations Associated with Death from Visceral Leishmaniasis
The visceral leishmaniasis (VL) is a disease potentially fatal if not diagnosed and treated opportunely. This article presents the results of the study on the manifestations identified at the time of the clinical suspicion of the VL cases. This study was conducted in Belo Horizonte, the capital of the State of Minas Gerais, located in southeastern Brazil. This study is both timely and substantive because the Belo Horizonte is an area of transmission of VL, with one of the highest VL-death proportions of Brazil. The patients with higher risk of death had at least one of the following characteristics: â„60 years, weakness, HIV co-infection, bleeding, jaundice and other associated infections. During the period 2002â2009, 8% to 22% of the patients with VL progressed to death in Belo Horizonte, whilst the proportion in the country was much lower and varied between 5% and 9%. This study has identified vulnerable patients who are at higher risk of death from VL and who would benefit from early predictive evaluation of the prognostic. Hence, the knowledge regarding the factors associated with death may contribute for clinical management and for reduction of deaths from VL
After surgery: the effects of life-saving caesarean sections in Burkina Faso:BMC Pregnancy Childbirth
Background
In African countries, caesarean sections are usually performed to save mothers and babiesâ lives, sometimes in extremis and at considerable costs. Little is known about the health and lives of women once discharged after such surgery. We investigated the long-term effects of life-saving caesarean section on health, economic and social outcomes in Burkina Faso.
Methods
We conducted a 4Â year prospective cohort study of women and their babies using mixed methods. The quantitative sample was selected in seven hospitals and included 950 women: 100 women with a caesarean section associated with near-miss complication (life-saving caesareans); 173 women with a vaginal birth associated with near-miss complication; and 677 women with uncomplicated vaginal childbirth. Structured interviews were conducted at 3Â months, 6Â months, 12Â months and 3 and 4Â years postpartum. These were supplemented by medical record data on delivery and physical examinations at 6 and 12Â months postpartum. The lives and experiences of 21 women were documented ethnographically. Data were analysed with multivariable logistic regressions, using survival analysis and thematic analysis.
Results
The physical effects of life-saving caesareans appeared to be similar to women who had an uncomplicated childbirth, although 55Â % of women with life-saving caesareans had another caesarean in their next pregnancy. The negative effects were generally economic, social and reproductive when compared to vaginal births, including increased debts (AORâ=â3.91 (1.46â10.48) and sexual violence (AORâ=â4.71 (1.04â21.3)) and lower fertility (AORâ=â0.44 (0.24â0.80)) 4Â years after life-saving caesareans. In the short and medium term, women with life-saving caesareans appeared to suffer increased psychological distress compared to uncomplicated births. They were more likely to use contraceptives (AORâ=â5.95 (1.53â23.06); 3Â months). Mortality of the index child was increased in both near-miss groups, independent of delivery mode. Ethnographic data suggest that these consequences are significant for Burkinabe women, whose well-being and social standing are mostly determined by their fertility, marriage strength and family links.
Conclusions
Life-saving caesareans have broad consequences beyond clinical sequelae. The recent policy to subsidise emergency obstetric care costs implemented in Burkina Faso should help avoid the majority of catastrophic costs, shown to be problematic for women undergoing emergency caesarean section
Patterns of ash (Fraxinus excelsior L.) colonization in mountain grasslands: the importance of management practices
International audienceWoody colonization of grasslands is often associated with changes in abiotic or biotic conditions or a combination of both. Widely used as fodder and litter in the past traditional agro-pastoral system, ash (Fraxinus excelsior L.) has now become a colonizing species of mountain grasslands in the French Pyrenees. Its present distribution is dependent on past human activities and it is locally controlled by propagule pressure and abiotic conditions. However, even when all favourable conditions are met, all the potentially colonizable grasslands are not invaded. We hypothesize that management practices should play a crucial role in the control of ash colonization. From empirical field surveys we have compared the botanical composition of a set of grasslands (present and former) differing in management practices and level of ash colonization. We have displayed a kind of successional gradient positively linked to both ash cover and height but not to the age of trees. We have tested the relationships between ash presence in grassland and management types i.e. cutting and/or grazing, management intensity and some grassland communities' features i.e. total and local specific richness and species heterogeneity. Mixed use (cutting and grazing) is negatively linked to ash presence in grassland whereas grazing alone positively. Mixed use and high grazing intensity are directly preventing ash seedlings establishment, when low grazing intensity is allowing ash seedlings establishment indirectly through herbaceous vegetation neglected by livestock. Our results show the existence of a limit between grasslands with and without established ashes corresponding to a threshold in the intensity of use. Under this threshold, when ash is established, the colonization process seems to become irreversible. Ash possesses the ability of compensatory growth and therefore under a high grazing intensity develops a subterranean vegetative reproduction. However the question remains at which stage of seedling development and grazing intensity these strategies could occur
The SuperCam Instrument Suite on the Mars 2020 Rover: Science Objectives and Mast-Unit Description
On the NASA 2020 rover mission to Jezero crater, the remote determination of the texture, mineralogy and chemistry of rocks is essential to quickly and thoroughly characterize an area and to optimize the selection of samples for return to Earth. As part of the Perseverance payload, SuperCam is a suite of five techniques that provide critical and complementary observations via Laser-Induced Breakdown Spectroscopy (LIBS), Time-Resolved Raman and Luminescence (TRR/L), visible and near-infrared spectroscopy (VISIR), high-resolution color imaging (RMI), and acoustic recording (MIC). SuperCam operates at remote distances, primarily 2-7 m, while providing data at sub-mm to mm scales. We report on SuperCam's science objectives in the context of the Mars 2020 mission goals and ways the different techniques can address these questions. The instrument is made up of three separate subsystems: the Mast Unit is designed and built in France; the Body Unit is provided by the United States; the calibration target holder is contributed by Spain, and the targets themselves by the entire science team. This publication focuses on the design, development, and tests of the Mast Unit; companion papers describe the other units. The goal of this work is to provide an understanding of the technical choices made, the constraints that were imposed, and ultimately the validated performance of the flight model as it leaves Earth, and it will serve as the foundation for Mars operations and future processing of the data.In France was provided by the Centre National d'Etudes Spatiales (CNES). Human resources were provided in part by the Centre National de la Recherche Scientifique (CNRS) and universities. Funding was provided in the US by NASA's Mars Exploration Program. Some funding of data analyses at Los Alamos National Laboratory (LANL) was provided by laboratory-directed research and development funds
Searches for Neutrinos from Gamma-Ray Bursts using the IceCube Neutrino Observatory
Gamma-ray bursts (GRBs) are considered as promising sources of
ultra-high-energy cosmic rays (UHECRs) due to their large power output.
Observing a neutrino flux from GRBs would offer evidence that GRBs are hadronic
accelerators of UHECRs. Previous IceCube analyses, which primarily focused on
neutrinos arriving in temporal coincidence with the prompt gamma rays, found no
significant neutrino excess. The four analyses presented in this paper extend
the region of interest to 14 days before and after the prompt phase, including
generic extended time windows and targeted precursor searches. GRBs were
selected between May 2011 and October 2018 to align with the data set of
candidate muon-neutrino events observed by IceCube. No evidence of correlation
between neutrino events and GRBs was found in these analyses. Limits are set to
constrain the contribution of the cosmic GRB population to the diffuse
astrophysical neutrino flux observed by IceCube. Prompt neutrino emission from
GRBs is limited to 1% of the observed diffuse neutrino flux, and
emission on timescales up to s is constrained to 24% of the total
diffuse flux
All-flavor constraints on nonstandard neutrino interactions and generalized matter potential with three years of IceCube DeepCore data
We report constraints on nonstandard neutrino interactions (NSI) from the observation of atmospheric neutrinos with IceCube, limiting all individual coupling strengths from a single dataset. Furthermore, IceCube is the first experiment to constrain flavor-violating and nonuniversal couplings simultaneously. Hypothetical NSI are generically expected to arise due to the exchange of a new heavy mediator particle. Neutrinos propagating in matter scatter off fermions in the forward direction with negligible momentum transfer. Hence the study of the matter effect on neutrinos propagating in the Earth is sensitive to NSI independently of the energy scale of new physics. We present constraints on NSI obtained with an all-flavor event sample of atmospheric neutrinos based on three years of IceCube DeepCore data. The analysis uses neutrinos arriving from all directions, with reconstructed energies between 5.6 GeV and 100 GeV. We report constraints on the individual NSI coupling strengths considered singly, allowing for complex phases in the case of flavor-violating couplings. This demonstrates that IceCube is sensitive to the full NSI flavor structure at a level competitive with limits from the global analysis of all other experiments. In addition, we investigate a generalized matter potential, whose overall scale and flavor structure are also constrained
Searching for High-energy Neutrino Emission from Galaxy Clusters with IceCube
Galaxy clusters have the potential to accelerate cosmic rays (CRs) to ultrahigh energies via accretion shocks or embedded CR acceleration sites. The CRs with energies below the Hillas condition will be confined within the cluster and eventually interact with the intracluster medium gas to produce secondary neutrinos and gamma rays. Using 9.5 yr of muon neutrino track events from the IceCube Neutrino Observatory, we report the results of a stacking analysis of 1094 galaxy clusters with masses âł10 Mâ and redshifts between 0.01 and âŒ1 detected by the Planck mission via the SunyaevâZelâdovich effect. We find no evidence for significant neutrino emission and report upper limits on the cumulative unresolved neutrino flux from massive galaxy clusters after accounting for the completeness of the catalog up to a redshift of 2, assuming three different weighting scenarios for the stacking and three different power-law spectra. Weighting the sources according to mass and distance, we set upper limits at a 90% confidence level that constrain the flux of neutrinos from massive galaxy clusters (âł10 Mâ) to be no more than 4.6% of the diffuse IceCube observations at 100 TeV, assuming an unbroken Eâ power-law spectrum
Strong Constraints on Neutrino Nonstandard Interactions from TeV-Scale Μ Disappearance at IceCube
We report a search for nonstandard neutrino interactions (NSI) using eight years of TeV-scale atmospheric muon neutrino data from the IceCube Neutrino Observatory. By reconstructing incident energies and zenith angles for atmospheric neutrino events, this analysis presents unified confidence intervals for the NSI parameter ΔΌÏ. The best-fit value is consistent with no NSI at a p value of 25.2%. With a 90% confidence interval of â0.0041â€Î”ÎŒÏâ€0.0031 along the real axis and similar strength in the complex plane, this result is the strongest constraint on any NSI parameter from any oscillation channel to date
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