67 research outputs found
GW190521 formation scenarios via relativistic accretion
The recent gravitational wave transient GW190521 has been interpreted by the
LIGO-Virgo collaboration (LVC) as sourced by a binary black hole (BH) merger.
According to the LVC parameter estimation, at least one of these progenitors
falls into the so-called pair-instability supernova mass gap. This raises the
important question of how and when these progenitors formed. In this paper we
use an accretion model with super-Eddington mass accretion rate obtained from
General Relativity hydrodynamics simulations to analyse the scenario wherein
the GW190521 original progenitors (OPs) formed at lower masses (and spins) and
grew to their estimated LVC parameters by relativistic accretion. We consider
that the environment wherein the binary is immersed has density gradients as
well as a dependence on the Mach number of the gas. Taking the LVC parameter
estimation at as the endpoint of the accretion evolution, we estimate
the initial masses and spins of the OPs at three different red-shifts $z=100, \
5020(i)10^{-4}
M_{\odot} - 3 M_{\odot}a_{\star}< 10^{-2}(ii)3 M_{\odot} - 40M_{\odot} 10^{-2} < a_{\star} < 0.5(iii)40M_{\odot}
- 70M_{\odot}a_{\star}\sim 0.5\sim 2\%$ ...Comment: 16 pages, 5 figures, 1 tabl
An Exact Homogeneous Stiff Cosmology that Reduces to the Kasner Solution
A family of exact simple solutions of Einstein field equations for homogeneous stiff cosmologies is presented. The method to obtain the solution is based on the introduction of auxiliary functions in order to cast the Einstein equations in such a way that can be explicitly integrated. The obtained solution is expressed in terms of simple functions of the used coordinates. The geometrical and kinematical properties of the solution are analyzed and the parameters are restricted in order to have a physically acceptable behavior. The solution is of the Petrov type I and presents a big-bang singularity. Now, for a particular value of one of the parameters, the solution is a vacuum solution of the Bianchi I type that reduces to the Kasner solution.
Se presenta una familia de soluciones exactas sencillas de las ecuaciones de Einstein homogéneas sobre el plano para las cosmologías rígidas. El método para obtener la solución se basa en la introducción de funciones auxiliares, a fin de emitir las ecuaciones de Einstein de tal manera que puedan ser integradas explícitamente. La solución obtenida se expresa en términos de funciones simples de las coordenadas utilizadas. Se analizan las propiedades geométricas y cinemáticas de la solución; los parámetros están restringidas a fin de tener un comportamiento aceptable físicamente. Las soluciones son del tipo Petrov I, y presentan una singularidad de big-bang. Ahora bien, para un cierto valor de uno de los parámetros la solución es una solución de vacío de tipo Bianchi I, que se reduce a la solución de Kasner.
 
Two Simple Families of Exact Inhomogeneous Stiff Cosmologies
Two families of exact simple solutions of Einstein field equations for inhomogeneous stiff cosmologies are presented. The method to obtain the solutions is based on the introduction of auxiliary functions in order to cast the Einstein equations in such a way that can be explicitly integrated. Although the equations are mathematically equivalent to the equations obtained when the source of matter is a scalar field, it is worth to mention that the source that we consider is not a scalar field but a perfect fluid with a stiff equation of state. The obtained solutions are expressed in terms of simple functions of the used coordinates and two families of particular solutions are considered. The geometrical and kinematical properties of the solutions are then analyzed and the parameters are restricted in order to have a physically acceptable behavior. The two particular solutions are of the Petrov type I, the first one being regular everywhere whereas the second one presents a big-bang singularity. Now, for a particular value of one of the parameters, the second particular solution is a vacuum solution of the Bianchi I type that reduces to the Kasner solution
Magnetised tori with magnetic polarisation around Kerr black holes: variable angular momentum discs
Analytical models of magnetised, geometrically thick discs are relevant to
understand the physical conditions of plasma around compact objects and to
explore its emitting properties. This has become increasingly important in
recent years in the light of the Event Horizon Telescope observations of Sgr A*
and M87. Models of thick discs around black holes usually consider constant
angular momentum distributions and do not take into account the magnetic
response of the fluid to applied magnetic fields. We present a generalisation
of our previous work on stationary models of magnetised accretion discs with
magnetic polarisation (Pimentel et al. 2018). This extension is achieved by
accounting for non-constant specific angular momentum profiles, done through a
two-parameter ansatz for those distributions. We build a large number of new
equilibrium solutions of thick discs with magnetic polarisation around Kerr
black holes, selecting suitable parameter values within the intrinsically
substantial parameter space of the models. We study the morphology and the
physical properties of those solutions, finding qualitative changes with
respect to the constant angular momentum tori of (Pimentel et al. 2018).
However, the dependences found on the angular momentum distribution or on the
black hole spin do not seem to be strong. Some of the new solutions, however,
exhibit a local maximum of the magnetisation function, absent in standard
magnetised tori. Due to the enhanced development of the magneto-rotational
instability as a result of magnetic susceptibility, those models might be
particularly well-suited to investigate jet formation through
general-relativistic MHD simulations. The new equilibrium solutions reported
here can be used as initial data in numerical codes to assess the impact of
magnetic susceptibility in the dynamics and observational properties of thick
disc-black hole systems.Comment: 15 pages, 8 figures. Comments welcom
Scalar Field Dark Matter: behavior around black holes
We present the numerical evolution of a massive test scalar fields around a
Schwarzschild space-time. We proceed by using hyperboloidal slices that
approach future null infinity, which is the boundary of scalar fields, and also
demand the slices to penetrate the event horizon of the black hole. This
approach allows the scalar field to be accreted by the black hole and to escape
toward future null infinity. We track the evolution of the energy density of
the scalar field, which determines the rate at which the scalar field is being
diluted. We find polynomial decay of the energy density of the scalar field,
and use it to estimate the rate of dilution of the field in time. Our findings
imply that the energy density of the scalar field decreases even five orders of
magnitude in time scales smaller than a year. This implies that if a
supermassive black hole is the Schwarzschild solution, then scalar field dark
matter would be diluted extremely fastComment: 15 pages, 21 eps figures. Appendix added, accepted for publication in
JCA
Association of kidney disease measures with risk of renal function worsening in patients with type 1 diabetes
Background: Albuminuria has been classically considered a marker of kidney damage progression in diabetic patients and it is routinely assessed to monitor kidney function. However, the role of a mild GFR reduction on the development of stage 653 CKD has been less explored in type 1 diabetes mellitus (T1DM) patients. Aim of the present study was to evaluate the prognostic role of kidney disease measures, namely albuminuria and reduced GFR, on the development of stage 653 CKD in a large cohort of patients affected by T1DM. Methods: A total of 4284 patients affected by T1DM followed-up at 76 diabetes centers participating to the Italian Association of Clinical Diabetologists (Associazione Medici Diabetologi, AMD) initiative constitutes the study population. Urinary albumin excretion (ACR) and estimated GFR (eGFR) were retrieved and analyzed. The incidence of stage 653 CKD (eGFR < 60 mL/min/1.73 m2) or eGFR reduction > 30% from baseline was evaluated. Results: The mean estimated GFR was 98 \ub1 17 mL/min/1.73m2 and the proportion of patients with albuminuria was 15.3% (n = 654) at baseline. About 8% (n = 337) of patients developed one of the two renal endpoints during the 4-year follow-up period. Age, albuminuria (micro or macro) and baseline eGFR < 90 ml/min/m2 were independent risk factors for stage 653 CKD and renal function worsening. When compared to patients with eGFR > 90 ml/min/1.73m2 and normoalbuminuria, those with albuminuria at baseline had a 1.69 greater risk of reaching stage 3 CKD, while patients with mild eGFR reduction (i.e. eGFR between 90 and 60 mL/min/1.73 m2) show a 3.81 greater risk that rose to 8.24 for those patients with albuminuria and mild eGFR reduction at baseline. Conclusions: Albuminuria and eGFR reduction represent independent risk factors for incident stage 653 CKD in T1DM patients. The simultaneous occurrence of reduced eGFR and albuminuria have a synergistic effect on renal function worsening
Hyperoxemia and excess oxygen use in early acute respiratory distress syndrome : Insights from the LUNG SAFE study
Publisher Copyright: © 2020 The Author(s). Copyright: Copyright 2020 Elsevier B.V., All rights reserved.Background: Concerns exist regarding the prevalence and impact of unnecessary oxygen use in patients with acute respiratory distress syndrome (ARDS). We examined this issue in patients with ARDS enrolled in the Large observational study to UNderstand the Global impact of Severe Acute respiratory FailurE (LUNG SAFE) study. Methods: In this secondary analysis of the LUNG SAFE study, we wished to determine the prevalence and the outcomes associated with hyperoxemia on day 1, sustained hyperoxemia, and excessive oxygen use in patients with early ARDS. Patients who fulfilled criteria of ARDS on day 1 and day 2 of acute hypoxemic respiratory failure were categorized based on the presence of hyperoxemia (PaO2 > 100 mmHg) on day 1, sustained (i.e., present on day 1 and day 2) hyperoxemia, or excessive oxygen use (FIO2 ≥ 0.60 during hyperoxemia). Results: Of 2005 patients that met the inclusion criteria, 131 (6.5%) were hypoxemic (PaO2 < 55 mmHg), 607 (30%) had hyperoxemia on day 1, and 250 (12%) had sustained hyperoxemia. Excess FIO2 use occurred in 400 (66%) out of 607 patients with hyperoxemia. Excess FIO2 use decreased from day 1 to day 2 of ARDS, with most hyperoxemic patients on day 2 receiving relatively low FIO2. Multivariate analyses found no independent relationship between day 1 hyperoxemia, sustained hyperoxemia, or excess FIO2 use and adverse clinical outcomes. Mortality was 42% in patients with excess FIO2 use, compared to 39% in a propensity-matched sample of normoxemic (PaO2 55-100 mmHg) patients (P = 0.47). Conclusions: Hyperoxemia and excess oxygen use are both prevalent in early ARDS but are most often non-sustained. No relationship was found between hyperoxemia or excessive oxygen use and patient outcome in this cohort. Trial registration: LUNG-SAFE is registered with ClinicalTrials.gov, NCT02010073publishersversionPeer reviewe
Goodbye Hartmann trial: a prospective, international, multicenter, observational study on the current use of a surgical procedure developed a century ago
Background: Literature suggests colonic resection and primary anastomosis (RPA) instead of Hartmann's procedure (HP) for the treatment of left-sided colonic emergencies. We aim to evaluate the surgical options globally used to treat patients with acute left-sided colonic emergencies and the factors that leading to the choice of treatment, comparing HP and RPA. Methods: This is a prospective, international, multicenter, observational study registered on ClinicalTrials.gov. A total 1215 patients with left-sided colonic emergencies who required surgery were included from 204 centers during the period of March 1, 2020, to May 31, 2020. with a 1-year follow-up. Results: 564 patients (43.1%) were females. The mean age was 65.9 ± 15.6 years. HP was performed in 697 (57.3%) patients and RPA in 384 (31.6%) cases. Complicated acute diverticulitis was the most common cause of left-sided colonic emergencies (40.2%), followed by colorectal malignancy (36.6%). Severe complications (Clavien-Dindo ≥ 3b) were higher in the HP group (P < 0.001). 30-day mortality was higher in HP patients (13.7%), especially in case of bowel perforation and diffused peritonitis. 1-year follow-up showed no differences on ostomy reversal rate between HP and RPA. (P = 0.127). A backward likelihood logistic regression model showed that RPA was preferred in younger patients, having low ASA score (≤ 3), in case of large bowel obstruction, absence of colonic ischemia, longer time from admission to surgery, operating early at the day working hours, by a surgeon who performed more than 50 colorectal resections. Conclusions: After 100 years since the first Hartmann's procedure, HP remains the most common treatment for left-sided colorectal emergencies. Treatment's choice depends on patient characteristics, the time of surgery and the experience of the surgeon. RPA should be considered as the gold standard for surgery, with HP being an exception
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