The Effects of Terrain Properties Upon the Small Crater Population Distribution at Giordano Bruno: Implications for Lunar Chronology

The distribution of impact craters on the ejecta of Giordano Bruno, a recent (<10 Ma) 22-km diameter crater within the lunar highlands, exhibits substantial variations. We surveyed craters D ≥ 10 m across a 1,323 km2 area of Giordano Bruno's ejecta and compared the distribution of craters with variations in thermophysical properties derived from the Lunar Reconnaissance Orbiter Diviner instrument. We used Diviner-derived rock abundance and nighttime regolith temperatures along with thermal model-predicted surface temperatures for a diversity of terrains to identify and isolate areas of the ejecta based on thermophysical properties such as bulk density and thermal conductivity. We found that thermophysical properties of the ejecta vary considerably both laterally and vertically, and consistently differ from typical regolith, indicating the presence of higher thermal inertia materials. Crater-size frequencies are significantly lower in areas with terrain properties exhibiting higher: rock abundance, nighttime temperatures, and/or modeled thermal inertia. This discrepancy in crater distribution increases for craters smaller than ∼25 m. These thermophysical variations indicate changes in the mechanical properties of the target materials. We suggest that these variations-specifically, terrain-dependent crater scaling variations and impactor-scale heterogeneities in material properties such as the presence or absence of large boulders-may influence crater diameters or inhibit crater production altogether in Giordano Bruno's ejecta; furthermore, these factors are size-dependent

Warfarin pharmacogenetics: development of a dosing algorithm for Omani patients

International audienceThe objective of our present study was to develop a warfarin dosing algorithm for the Omani patients, as performances of warfarin dosing algorithms vary across populations with impact on the daily maintenance dose. We studied the functional polymorphisms of CYP2C9, CYP4F2 and VKORC1 genes to evaluate their impact on the warfarin maintenance dose in an admixed Omani patient cohort with Caucasian, African and Asian ancestries. We observed a 64-fold inter-patient variability for warfarin to achieve stable international normalized ratio in these patients. Univariate analysis revealed that age, gender, weight, atrial fibrillation, deep vein thrombosis/pulmonary embolism and variant genotypes of CYP2C9 and VKORC1 loci were significantly associated with warfarin dose in the studied patient population. However, multiple regression model showed that only the atrial fibrillation, and homozygous CYP2C9 variant genotypes (*2/*3 and *3/*3) and VKORC1 GA and AA genotypes remained significant. A multivariate model, which included demographic, clinical and pharmacogenetic variables together explained 63% of the overall inter-patient variability in warfarin dose requirement in this microgeographically defined, ethnically admixed Omani patient cohort on warfarin. This locally developed model performed much better than the International Warfarin Pharmacogenetics Consortium (IWPC) model as the latter could only explain 34% of the inter-patient variability in Omani patients. VKORC1 3673G>A polymorphism emerged as the single most important predictor of warfarin dose variability, even in this admixed population (partial R(2)=0.45)

Composition and structure of the shallow subsurface of Ceres revealed by crater morphology

Before NASA’s Dawn mission, the dwarf planet Ceres was widely believed to contain a substantial ice-rich layer below its rocky surface. The existence of such a layer has significant implications for Ceres’s formation, evolution, and astrobiological potential. Ceres is warmer than icy worlds in the outer Solar System and, if its shallow subsurface is ice-rich, large impact craters are expected to be erased by viscous flow on short geologic timescales. Here we use digital terrain models derived from Dawn Framing Camera images to show that most of Ceres’s largest craters are several kilometres deep, and are therefore inconsistent with the existence of an ice-rich subsurface. We further show from numerical simulations that the absence of viscous relaxation over billion-year timescales implies a subsurface viscosity that is at least one thousand times greater than that of pure water ice. We conclude that Ceres’s shallow subsurface is no more than 30% to 40% ice by volume, with a mixture of rock, salts and/or clathrates accounting for the other 60% to 70%. However, several anomalously shallow craters are consistent with limited viscous relaxation and may indicate spatial variations in subsurface ice content