The formation of giant planets in wide orbits by photoevaporation-synchronised migration

The discovery of giant planets in wide orbits represents a major challenge for planet formation theory. In the standard core accretion paradigm planets are expected to form at radial distances $\lesssim 20$ au in order to form massive cores (with masses $\gtrsim 10~\textrm{M}_{\oplus}$) able to trigger the gaseous runaway growth before the dissipation of the disc. This has encouraged authors to find modifications of the standard scenario as well as alternative theories like the formation of planets by gravitational instabilities in the disc to explain the existence of giant planets in wide orbits. However, there is not yet consensus on how these systems are formed. In this letter, we present a new natural mechanism for the formation of giant planets in wide orbits within the core accretion paradigm. If photoevaporation is considered, after a few Myr of viscous evolution a gap in the gaseous disc is opened. We found that, under particular circumstances planet migration becomes synchronised with the evolution of the gap, which results in an efficient outward planet migration. This mechanism is found to allow the formation of giant planets with masses $M_p\lesssim 1 M_{\rm Jup}$ in wide stable orbits as large as $\sim$130 au from the central star.Comment: Accepted for publication in MNRAS Letters. Comments are welcom

Terrestrial-type planet formation: Comparing different types of initial conditions

To study the terrestrial-type planet formation during the post oligarchic growth, the initial distributions of planetary embryos and planetesimals used in N-body simulations play an important role. Most of these studies typically use ad hoc initial distributions based on theoretical and numerical studies. We analyze the formation of planetary systems without gas giants around solar-type stars focusing on the sensitivity of the results to the particular initial distributions of planetesimals and embryos. The formation of terrestrial planets in the habitable zone (HZ) and their final water contents are topics of interest. We developed two different sets of N-body simulations from the same protoplanetary disk. The first set assumes ad hoc initial distributions for embryos and planetesimals and the second set obtains these distributions from the results of a semi-analytical model which simulates the evolution of the gaseous phase of the disk. Both sets form planets in the HZ. Ad hoc initial conditions form planets in the HZ with masses from $0.66M_{\oplus}$ to $2.27M_{\oplus}$. More realistic initial conditions obtained from a semi-analytical model, form planets with masses between $1.18M_{\oplus}$ and $2.21M_{\oplus}$. Both sets form planets in the HZ with water contents between 4.5% and 39.48% by mass. Those planets with the highest water contents respect to those with the lowest, present differences regarding the sources of water supply. We suggest that the number of planets in the HZ is not sensitive to the particular initial distribution of embryos and planetesimals and thus, the results are globally similar between both sets. However, the main differences are associated to the accretion history of the planets in the HZ. These discrepancies have a direct impact in the accretion of water-rich material and in the physical characteristics of the resulting planets.Comment: Accepted for publication in Astronomy and Astrophysics, 13 pages, 9 figure

Chemical composition of Earth-like planets

Models of planet formation are mainly focused on the accretion and dynamical processes of the planets, neglecting their chemical composition. In this work, we calculate the condensation sequence of the different chemical elements for a low-mass protoplanetary disk around a solar-type star. We incorporate this sequence of chemical elements (refractory and volatile elements) in our semi-analytical model of planet formation which calculates the formation of a planetary system during its gaseous phase. The results of the semi-analytical model (final distributions of embryos and planetesimals) are used as initial conditions to develope N-body simulations that compute the post-oligarchic formation of terrestrial-type planets. The results of our simulations show that the chemical composition of the planets that remain in the habitable zone has similar characteristics to the chemical composition of the Earth. However, exist differences that can be associated to the dynamical environment in which they were formed.Comment: 3 pages, 4 figures - Accepted for publication in the Bolet\'in de la Asociaci\'on Argentina de Astronom\'ia, vol.5

Opportunities from low-resolution modelling of river morphology in remote parts of the world

Abstract. River morphodynamics are the result of a variety of processes, ranging from the typical small-scale of fluid mechanics (e.g. flow turbulence dissipation) to the large-scale of landscape evolution (e.g. fan deposition). However, problems inherent in the long-term modelling of large rivers derive from limited computational resources and the high level of process detail (i.e. spatial and temporal resolution). These modelling results depend on processes parameterization and calibrations based on detailed field data (e.g. initial morphology). Thus, for these cases, simplified tools are attractive. In this paper, a simplified 1-D approach is presented that is suited for modelling very large rivers. A synthetic description of the variations of cross-sections shapes is implemented on the basis of satellite images, typically also available for remote parts of the world. The model's flexibility is highlighted here by presenting two applications. In the first case, the model is used for analysing the long-term evolution of the lower Zambezi River (Africa) as it relates to the construction of two reservoirs for hydropower exploitation. In the second case, the same model is applied to study the evolution of the middle and lower Paraná River (Argentina), particularly in the context of climate variability. In both cases, having only basic data for boundary and initial conditions, the 1-D model provides results that are in agreement with past studies and therefore shows potential to be used to assist sediment management at the watershed scale or at boundaries of more detailed models

Effect of mixtures of pesticides used in the direct seeding technique on nontarget plant seeds

The objective of the present study was to assess the effects on germination and root elongation of seeds exposed to the Roundup Max formulation of the glyphosate herbicide and the formulations Shooter and Sherpa of tiie insecticides chlorpyrifos and cypermethrin, separately and all of then- possible mixtures in imbibition solutions. Effects of environmental samples from crop fields are also analyzed.Centro de Investigaciones del Medio Ambient

Rationale for Medium Cutoff Membranes in COVID-19 Patients Requiring Renal Replacement Therapy

The current pandemic of coronavirus disease 2019 (COVID-19) spotlighted the vulnerability of patients with chronic kidney disease stage 5 on maintenance hemodialysis (HD) to the viral infection. Social distancing is the most effective preventive measure to reduce the risk of infection. Nonetheless, the necessity to frequently reach the dialysis center and the inherent social gathering both impede social distancing and also self-quarantine for infected individuals. A baseline hyperinflammatory state driven by factors such as the retention of uremic toxins afflicts these patients. Concomitantly, a condition of relative immunosuppression is also attributed to similar factors. The use of high-flux (HF) dialyzers for HD is the standard of care. However, with HF membranes, the removal of large middle molecules is scant. Medium cutoff (MCO) dialyzers are a new class of membranes that allow substantial removal of large middle molecules with negligible albumin losses. Recent trials confirmed long-term safety and long-term sustained reduction in the concentration of large uremic toxins with MCO dialyzers. Herein, we discuss the rationale for applying MCO membranes in COVID-19 patients and its possible immunoadjuvant effects that could mitigate the burden of COVID-19 infection in dialysis patients. We also discuss the direct cytopathic effect of the virus on renal tissue and extracorporeal blood purification techniques that can prevent kidney damage or reduce acute kidney injury progression

Peritoneal Dialysis for Chronic Congestive Heart Failure

Maladaptive responses between a failing heart and the kidneys ultimately lead to permanent chronic kidney disease, referred to as cardiorenal syndrome type 2. In this narrative review, we discuss the pathophysiological pathways in the progression of cardiorenal failure and review the current evidence on peritoneal dialysis as a treatment strategy in cardiorenal syndrome type 2. A patient with heart failure can present with clinical symptoms related to venous congestion even in the absence of end-stage renal disease. Diuretics remain the cornerstone for the treatment of fluid overload related to heart failure. However, with chronic use, diuretic resistance can supervene. When medical therapy is no longer able to relieve congestive symptoms, ultrafiltration might be needed. Patients with heart failure tolerate well the gentle rate of fluid removal through peritoneal dialysis. Recent publications suggest a positive impact of starting peritoneal dialysis in patients with cardiorenal syndrome type 2 on the hospitalisation rate, functional status and quality of life

Most super-Earths formed by dry pebble accretion are less massive than 5 Earth masses

We study the formation of rocky planets by dry pebble accretion from self-consistent dust-growth models. In particular, we aim at computing the maximum core mass of a rocky planet that can sustain a thin H-He atmosphere to account for the second peak of the Kepler's size distribution. We simulate planetary growth by pebble accretion inside the ice line. The pebble flux is computed self-consistently from dust growth by solving the advection-diffusion equation for a representative dust size. Dust coagulation, drift, fragmentation and sublimation at the water iceline are included. The disc evolution is computed for $\alpha$-discs with photoevaporation from the central star. The planets grow from a moon-mass embryo by silicate pebble accretion and gas accretion. We analyse the effect of a different initial disc mass, $\alpha$-viscosity, disc metallicity and embryo location. Finally, we compute atmospheric mass-loss due to evaporation. We find that inside the ice line, the fragmentation barrier determines the size of pebbles, which leads to different planetary growth patterns for different disc viscosities. Within the iceline the pebble isolation mass typically decays to values below 5 M$_{\oplus}$ within the first million years of disc evolution, limiting the core masses to that value. After computing atmospheric-mass loss, we find that planets with cores below $\sim$4 M$_{\oplus}$ get their atmospheres completely stripped, and a few 4-5 M$_{\oplus}$ cores retain a thin atmosphere that places them in the gap/second peak of the Kepler size distribution. Overall, we find that rocky planets form only in low-viscosity discs ($\alpha \lesssim 10^{-4}$). When $\alpha \geq 10^{-3}$, rocky objects do not grow beyond Mars-mass. The most typical outcome of dry pebble accretion is terrestrial planets with masses spanning from Mars to $\sim$4 M$_{\oplus}$.Comment: Accepted for publication in A&