Mantle redox state drives outgassing chemistry and atmospheric composition of rocky planets.

Volcanic degassing of planetary interiors has important implications for their corresponding atmospheres. The oxidation state of rocky interiors affects the volatile partitioning during mantle melting and subsequent volatile speciation near the surface. Here we show that the mantle redox state is central to the chemical composition of atmospheres while factors such as planetary mass, thermal state, and age mainly affect the degassing rate. We further demonstrate that mantle oxygen fugacity has an effect on atmospheric thickness and that volcanic degassing is most efficient for planets between 2 and 4 Earth masses. We show that outgassing of reduced systems is dominated by strongly reduced gases such as [Formula: see text], with only smaller fractions of moderately reduced/oxidised gases ([Formula: see text], [Formula: see text]). Overall, a reducing scenario leads to a lower atmospheric pressure at the surface and to a larger atmospheric thickness compared to an oxidised system. Atmosphere predictions based on interior redox scenarios can be compared to observations of atmospheres of rocky exoplanets, potentially broadening our knowledge on the diversity of exoplanetary redox states.

The dependence of the ice-albedo feedback on atmospheric properties.

Ice-albedo feedback is a potentially important destabilizing effect for the climate of terrestrial planets. It is based on the positive feedback between decreasing surface temperatures, an increase of snow and ice cover, and an associated increase in planetary albedo, which then further decreases surface temperature. A recent study shows that for M stars, the strength of the ice-albedo feedback is reduced due to the strong spectral dependence of stellar radiation and snow/ice albedos; that is, M stars primarily emit in the near IR, where the snow and ice albedo is low, and less in the visible, where the snow/ice albedo is high. This study investigates the influence of the atmosphere (in terms of surface pressure and atmospheric composition) on this feedback, since an atmosphere was neglected in previous studies. A plane-parallel radiative transfer model was used for the calculation of planetary albedos. We varied CO2 partial pressures as well as the H2O, CH4, and O3 content in the atmosphere for planets orbiting Sun-like and M type stars. Results suggest that, for planets around M stars, the ice-albedo effect is significantly reduced, compared to planets around Sun-like stars. Including the effects of an atmosphere further suppresses the sensitivity to the ice-albedo effect. Atmospheric key properties such as surface pressure, but also the abundance of radiative trace gases, can considerably change the strength of the ice-albedo feedback. For dense CO2 atmospheres of the order of a few to tens of bar, atmospheric rather than surface properties begin to dominate the planetary radiation budget. At high CO2 pressures, the ice-albedo feedback is strongly reduced for planets around M stars. The presence of trace amounts of H2O and CH4 in the atmosphere also weakens the ice-albedo effect for both stellar types considered. For planets around Sun-like stars, O3 could also lead to a very strong decrease of the ice-albedo feedback at high CO2 pressures.

An economic analysis of kidney transplantation.

Kidney transplantation is the most cost-effective treatment modality for end-stage renal disease (ESRD). Nonetheless, in keeping with the managed care mandate, expense has become an increasingly significant issue. Over $11 billion is now spent each year on ESRD treatment. Medicare per capita annual payments exceed $36,000 per beneficiary. Transplant procedure charges and outcomes vary dramatically across the United States. The average charge for a kidney transplant is approximately $82,000. Graft and patient survival rates are highly variable, even among the most active programs in the US. Individual transplant programs must implement approaches to contain their costs and assure quality. At the Mayo Clinic, our mean charge for a kidney transplant ($53,510) in 1996 was 27.2% below expected, given national medical inflation over the past decade. Unfortunately, the net operating income associated with our kidney transplant program has been severely eroded in an increasingly brutal economic environment.

Contracting for services: liver transplantation in the era of mismanaged care.

It is no secret that the health care environment today is motivated by the underlying, largely economic impetus of managed care. This is particularly evident within the organ transplantation community, where third party payers hope to minimize their financial risk by relying more and more on "centers of excellence" networks to provide high-quality transplant services in an economically efficient manner. The burgeoning interest in the economics of liver transplantation raises a number of complex, yet important, issues to which transplant professionals should lend serious thought. This article addresses these issues by offering an elementary guide to contract negotiations with third party payers. Among other things, the article: (1) discusses several methods by which third party payers avert and shift risk to transplant programs; (2) emphasizes the importance and identifies the limitations of actuaries and other consulting; (3) demonstrates, with examples, how comparative analyses of existing data sources, both public and proprietary, can assist rational decision-making.