Pluto's lower atmosphere and pressure evolution from ground-based stellar occultations, 1988-2016

Context. The tenuous nitrogen (N2) atmosphere on Pluto undergoes strong seasonal effects due to high obliquity and orbital eccentricity, and has recently (July 2015) been observed by the New Horizons spacecraft. Aims. The main goals of this study are (i) to construct a well calibrated record of the seasonal evolution of surface pressure on Pluto and (ii) to constrain the structure of the lower atmosphere using a central flash observed in 2015. Methods. Eleven stellar occultations by Pluto observed between 2002 and 2016 are used to retrieve atmospheric profiles (density, pressure, temperature) between altitude levels of ~5 and ~380 km (i.e. pressures from ~ 10 μbar to 10 nbar). Results. (i) Pressure has suffered a monotonic increase from 1988 to 2016, that is compared to a seasonal volatile transport model, from which tight constraints on a combination of albedo and emissivity of N2 ice are derived. (ii) A central flash observed on 2015 June 29 is consistent with New Horizons REX profiles, provided that (a) large diurnal temperature variations (not expected by current models) occur over Sputnik Planitia; and/or (b) hazes with tangential optical depth of ~0.3 are present at 4–7 km altitude levels; and/or (c) the nominal REX density values are overestimated by an implausibly large factor of ~20%; and/or (d) higher terrains block part of the flash in the Charon facing hemisphere

Influence of ferroalloy impurities and ferroalloy addition sequence on ultra low carbon (ULC) steel cleanliness after RH treatment

The present work outlines the statistical analysis of industrial data collected for a few hundred heats from an integrated steel plant. The main purpose was to study the influence of impurities in the ferroalloys FeTi (FeTi70 and FeTi35) and FeP on steel cleanliness. Therefore, two steel grades [ultra low carbon (ULC) high Mn and ULC low Mn] to which these ferroalloys are added were chosen for the study. The number of Al based inclusions analysed with pulse discrimination analysis-optical emission spectroscopy was taken as a measure of steel cleanliness and compared using box plot analysis and through a t test for different grades of FeTi additions. The ferroalloy parameters as well as other major process parameters during secondary metallurgy were also correlated to the inclusion number density. The statistical analysis was supplemented with elemental (ferroalloy) recovery calculations based on the industrial data and FactSage, the equilibrium Fe-Al-P-O diagram and the inclusion extraction analysis. On the basis of this study, it is proposed that (1) FeTi70 is a comparatively cleaner ferroalloy than FeTi35 and (2) for FeP in ULC low carbon steel, the best addition practice to maintain a balance between P recovery and steel cleanliness is towards the end of decarburisation and before the addition of Al blocks. © 2012 Institute of Materials, Minerals and Mining.status: publishe

Autochtonen en allochtonen samen op de werkvloer: uitdagingen en oplossingen

status: publishe