To predict the future contributions of the Antarctic ice sheets to sea-level rise, numerical models use reconstructions of past ice-sheet retreat after the Last Glacial Maximum to tune model ...parameters
. Reconstructions of the West Antarctic Ice Sheet have assumed that it retreated progressively throughout the Holocene epoch (the past 11,500 years or so)
. Here we show, however, that over this period the grounding line of the West Antarctic Ice Sheet (which marks the point at which it is no longer in contact with the ground and becomes a floating ice shelf) retreated several hundred kilometres inland of today's grounding line, before isostatic rebound caused it to re-advance to its present position. Our evidence includes, first, radiocarbon dating of sediment cores recovered from beneath the ice streams of the Ross Sea sector, indicating widespread Holocene marine exposure; and second, ice-penetrating radar observations of englacial structure in the Weddell Sea sector, indicating ice-shelf grounding. We explore the implications of these findings with an ice-sheet model. Modelled re-advance of the grounding line in the Holocene requires ice-shelf grounding caused by isostatic rebound. Our findings overturn the assumption of progressive retreat of the grounding line during the Holocene in West Antarctica, and corroborate previous suggestions of ice-sheet re-advance
. Rebound-driven stabilizing processes were apparently able to halt and reverse climate-initiated ice loss. Whether these processes can reverse present-day ice loss
on millennial timescales will depend on bedrock topography and mantle viscosity-parameters that are difficult to measure and to incorporate into ice-sheet models.
Context.
Fast rotation is responsible for important changes in the structure and evolution of stars and the way we see them. Optical long baseline interferometry now allows for the study of its ...effects on the stellar surface, mainly gravity darkening and flattening.
Aims.
We aim to determine the fundamental parameters of the fast-rotating star Altair, in particular its evolutionary stage (represented here by the core hydrogen mass fraction
X
c
), mass, and differential rotation, using state-of-the-art stellar interior and atmosphere models together with interferometric (ESO-VLTI), spectroscopic, and asteroseismic observations.
Methods.
We use ESTER two-dimensional stellar models to produce the relevant surface parameters needed to create intensity maps from atmosphere models. Interferometric and spectroscopic observables are computed from these intensity maps and several stellar parameters are then adjusted using the publicly available MCMC algorithm Emcee.
Results.
We determined Altair’s equatorial radius to be
R
eq
= 2.008 ± 0.006
R
⊙
, the position angle PA = 301.1 ± 0.3°, the inclination
i
= 50.7 ± 1.2°, and the equatorial angular velocity Ω = 0.74 ± 0.01 times the Keplerian angular velocity at equator. This angular velocity leads to a flattening of
ε
= 0.220 ± 0.003. We also deduce from the spectroscopically derived
v
sin
i
≃ 243 km s
−1
, a true equatorial velocity of ∼314 km s
−1
corresponding to a rotation period of 7h46m (∼3 cycles/day). The data also impose a strong correlation between mass, metallicity, hydrogen abundance, and core evolution. Thanks to asteroseismic data, and provided our frequencies identification is correct, we constrain the mass of Altair to 1.86 ± 0.03
M
⊙
and further deduce its metallicity
Z
= 0.019 and its core hydrogen mass fraction
X
c
= 0.71, assuming an initial solar hydrogen mass fraction
X
= 0.739. These values suggest that Altair is a young star ∼100 Myr old. Finally, the 2D ESTER model also gives the internal differential rotation of Altair, showing that its core rotates approximately 50% faster than the envelope, while the surface differential rotation does not exceed 6%.
ABSTRACT
We present the first asteroseismic results for δ Scuti and γ Doradus stars observed in Sectors 1 and 2 of the TESS mission. We utilize the 2-min cadence TESS data for a sample of 117 stars ...to classify their behaviour regarding variability and place them in the Hertzsprung–Russell diagram using Gaia DR2 data. Included within our sample are the eponymous members of two pulsator classes, γ Doradus and SX Phoenicis. Our sample of pulsating intermediate-mass stars observed by TESS also allows us to confront theoretical models of pulsation driving in the classical instability strip for the first time and show that mixing processes in the outer envelope play an important role. We derive an empirical estimate of 74 per cent for the relative amplitude suppression factor as a result of the redder TESS passband compared to the Kepler mission using a pulsating eclipsing binary system. Furthermore, our sample contains many high-frequency pulsators, allowing us to probe the frequency variability of hot young δ Scuti stars, which were lacking in the Kepler mission data set, and identify promising targets for future asteroseismic modelling. The TESS data also allow us to refine the stellar parameters of SX Phoenicis, which is believed to be a blue straggler.
The availability of direct‐acting antiviral agents for the treatment of hepatitis C virus (HCV) infection has resulted in a profound shift in the approach to the management of this infection. These ...changes have affected the practice of solid organ transplantation by altering the framework by which patients with end‐stage organ disease are managed and receive organ transplants. The high level of safety and efficacy of these medications in patients with chronic HCV infection provides the opportunity to explore their use in the setting of transplanting organs from HCV‐viremic patients into non–HCV‐viremic recipients. Because these organs are frequently discarded and typically come from younger donors, this approach has the potential to save lives on the solid organ transplant waitlist. Therefore, an urgent need exists for prospective research protocols that study the risk versus benefit of using organs for hepatitis C–infected donors. In response to this rapidly changing practice and the need for scientific study and consensus, the American Society of Transplantation convened a meeting of experts to review current data and develop the framework for the study of using HCV viremic organs in solid organ transplantation.
This article summarizes key points from a recent multidisciplinary meeting addressing the expansion of transplanting hepatitis C virus–infected donor organs in solid organ recipients. Fishman and Forns respond in an editorial on page 2755, and the conversation continues in the Letters to the Editor section (pages 2986, 2988, 2989).
Over the past two decades, live kidney donation by older individuals (≥55 years) has become more common. Given the strong associations of older age with cardiovascular disease (CVD), nephrectomy ...could make older donors vulnerable to death and cardiovascular events. We performed a cohort study among older live kidney donors who were matched to healthy older individuals in the Health and Retirement Study. The primary outcome was mortality ascertained through national death registries. Secondary outcomes ascertained among pairs with Medicare coverage included death or CVD ascertained through Medicare claims data. During the period from 1996 to 2006, there were 5717 older donors in the United States. We matched 3368 donors 1:1 to older healthy nondonors. Among donors and matched pairs, the mean age was 59 years; 41% were male and 7% were black race. In median follow‐up of 7.8 years, mortality was not different between donors and matched pairs (p = 0.21). Among donors with Medicare, the combined outcome of death/CVD (p = 0.70) was also not different between donors and nondonors. In summary, carefully selected older kidney donors do not face a higher risk of death or CVD. These findings should be provided to older individuals considering live kidney donation.
In this matched cohort study, 3,368 older (≥55 years) live kidney donors in the United States have no difference in mortality, cardiovascular disease, or diabetes rates compared to healthy older nondonors.
Deceased donor kidneys with acute kidney injury (AKI) are often discarded due to fear of poor outcomes. We performed a multicenter study to determine associations of AKI (increasing ...admission‐to‐terminal serum creatinine by AKI Network stages) with kidney discard, delayed graft function (DGF) and 6‐month estimated glomerular filtration rate (eGFR). In 1632 donors, kidney discard risk increased for AKI stages 1, 2 and 3 (compared to no AKI) with adjusted relative risks of 1.28 (1.08–1.52), 1.82 (1.45–2.30) and 2.74 (2.0–3.75), respectively. Adjusted relative risk for DGF also increased by donor AKI stage: 1.27 (1.09–1.49), 1.70 (1.37–2.12) and 2.25 (1.74–2.91), respectively. Six‐month eGFR, however, was similar across AKI categories but was lower for recipients with DGF (48 interquartile range: 31–61 vs. 58 45–75 ml/min/1.73m2 for no DGF, p < 0.001). There was significant favorable interaction between donor AKI and DGF such that 6‐month eGFR was progressively better for DGF kidneys with increasing donor AKI (46 29–60, 49 32–64, 52 36–59 and 58 39–71 ml/min/1.73m2 for no AKI, stage 1, 2 and 3, respectively; interaction p = 0.05). Donor AKI is associated with kidney discard and DGF, but given acceptable 6‐month allograft function, clinicians should consider cautious expansion into this donor pool.
This multicenter cohort study shows that clinically defined acute kidney injury in deceased donors is associated with kidney discarding as well as delayed graft function, but that the transplanted kidneys tend to have acceptable 6‐month function.
Aims.
We present the Rotation code Using Barotropy conservation over Isopotential Surfaces (RUBIS), a fully Python-based centrifugal deformation program that is available publicly. The code has been ...designed to calculate the centrifugal deformation of stars and planets resulting from a given cylindrical rotation profile, starting from a spherically symmetric non-rotating model.
Methods.
The underlying assumption in RUBIS is that the relation between density and pressure is preserved during the deformation process. This leads to many procedural simplifications. For instance, RUBIS only needs to solve Poisson’s equation in either spheroidal or spherical coordinates, depending on whether the 1D model has discontinuities.
Results.
We present the benefits of using RUBIS to deform polytropic models and more complex barotropic structures, thus providing insights into baroclinic models to a certain extent. The resulting structures can be used for a wide range of applications, including the seismic study of models. Finally, we illustrate how RUBIS is beneficial specifically in the analysis of Jupiter’s gravitational moments through its ability to handle discontinuous models while retaining a high accuracy compared to current methods.
Guidelines recommend restricting simultaneous liver–kidney (SLK) transplant to candidates with prolonged dialysis or estimated glomerular filtration rate (eGFR) <30 mL/min/1.73m2 for 90 days. ...However, few studies exist to support the latter recommendation. Using Scientific Registry of Transplant Recipients and Medicare dialysis data, we assembled a cohort of 4997 liver transplant recipients from February 27, 2002–January 1, 2008. Serial eGFRs were calculated from serum creatinines submitted with MELD reports. We categorized recipients by eGFR patterns in the 90 days pretransplant: Group 1 (eGFR always >30), Group 2 (eGFR fluctuated), Group 3 (eGFR always <30) and Group 4 (short‐term dialysis). For Group 2, we characterized fluctuations in renal function using time‐weighted mean eGFR. Among liver‐alone recipients in Group 3, the rate of end‐stage renal disease (ESRD) by 3 years was 31%, versus <10% for other groups (p < 0.001). In multivariable Cox regression, eGFR Group, diabetes (HR 2.65, p < 0.001) and black race (HR 1.83, p = 0.02) were associated with ESRD. Among liver‐alone recipients in Group 2, only diabetics with time‐weighted mean eGFR <30 had a substantial ESRD risk (25.6%). In summary, among liver transplant candidates not on prolonged dialysis, SLK should be considered for those whose eGFR is always <30 and diabetic candidates whose weighted mean eGFR is <30 for 90 days.
This study of linked registry and Medicare claims data demonstrates that for liver transplant recipients with kidney dysfunction, the risk of end‐stage renal disease is low unless the estimated glomerular filtration rate is consistently below 30, or confounded by diabetes. See editorial by Feng and Trotter on page 2869.
Context. Convective regions in stellar models are always associated with uncertainties, for example, due to extra-mixing or the possible inaccurate position of the transition from convective to ...radiative transport of energy. Such inaccuracies have a strong impact on stellar models and the fundamental parameters we derive from them. The most promising method to reduce these uncertainties is to use asteroseismology to derive appropriate diagnostics probing the structural characteristics of these regions. Aims. We wish to use custom-made integrated quantities to improve the capabilities of seismology to probe convective regions in stellar interiors. By doing so, we hope to increase the number of indicators obtained with structural seismic inversions to provide additional constraints on stellar models and the fundamental parameters we determine from theoretical modeling. Methods. First, we present new kernels associated with a proxy of the entropy in stellar interiors. We then show how these kernels can be used to build custom-made integrated quantities probing convective regions inside stellar models. We present two indicators suited to probe convective cores and envelopes, respectively, and test them on artificial data. Results. We show that it is possible to probe both convective cores and envelopes using appropriate indicators obtained with structural inversion techniques. These indicators provide direct constraints on a proxy of the entropy of the stellar plasma, sensitive to the characteristics of convective regions. These constraints can then be used to improve the modeling of solar-like stars by providing an additional degree of selection of models obtained from classical forward modeling approaches. We also show that in order to obtain very accurate indicators, we need ℓ = 3 modes for the envelope but that the core-conditions indicator is more flexible in terms of the seismic data required for its use.
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