Revealing the “fingerprints” of the magnetic precursor of C-shocks

We present the first C-shock and radiative transfer model that calculates the evolution of the line profiles of neutral and ion species like SiO, H¹³CO⁺ and HN¹³C for different flow times along the propagation of the shock through the unperturbed gas. We find that the line profiles of SiO characteristic of the magnetic precursor stage have very narrow linewidths and are centered at velocities close to the ambient cloud velocity, as observed toward the young shocks in the L1448-mm outflow. Consistently with previous works, our model also reproduces the broad SiO emission detected in the high velocity gas in this outflow, for the downstream postshock gas in the shock. This implies that the different velocity components observed in L1448-mm are due to the coexistence of different shocks at different evolutionary stages.     

Probabilistic Analysis of Suture Lines Developed in Ammonites: The Jurassic Examples of Hildocerataceae and Hammatocerataceae

Ammonites are extinct molluscs belonging to Class Cephalopoda which lived during the Mesozoic Era. Their usefulness in Jurassic and Cretaceous paleontology and biostratigraphy studies has been widely proved. They have been studied by several authors worldwide to achieve information regarding their habitats and the climate of the world in past eras. A probabilistic analysis of the paleo-environmental causes that generated complex suture lines in ammonites has been made by means of coherent upper conditional previsions defined with respect to Hausdorff outer measures. In particular, studies have centered on the role of hydrostatic pressure.     

The use of model compounds to investigate the release of covalently bound biomarkers via hydropyrolysis

This study describes the reduction of functionalised model compounds to their corresponding hydrocarbons by catalytic hydropyrolysis to provide information on the release of biomarkers from kerogens and asphaltenes covalently bound through the functional groups investigated. Five model compounds were investigated, the n-C₁₈ carboxylic acids, stearic and oleic acids; the C₂₄ steroidal acid, 5β-cholanic acid; and the saturated and unsaturated C₂₇ sterols, 5α-cholestanol and cholesterol. The yield and distribution of the hydrocarbons generated were assessed for the model compounds adsorbed to silica and carbon substrates, and unsupported on a bed of catalyst. The n-C₁₈ acids are shown to be reduced to the n-C₁₈ alkane, with a selectivity of >95% for stearic acid, although due to its unsaturated structure, oleic acid is prone to cracking, with shorter chained n-alkanes also being formed. The conversion of these compounds, adsorbed to either silica or carbon is relatively low, even at hydropyrolysis temperatures significantly above their boiling point, suggesting that interactions between the acids and substrate leading to the formation of stable entities (Si–O–C linkages in the case of silica) significantly retard volatilisation. The yield can be increased by placing the compounds directly onto a bed of catalyst, but for low boiling compounds such as stearic acid this can result in volatilisation and cracking at temperatures below that of the activation point of the catalyst. This method produced improved yields of >95% pure product for higher boiling compounds such as 5β-cholanic acid. The presence of the functional group attached to the ring system of compounds such as 5α-cholestanol does not diminish the selectivity of the technique. The double bond in cholesterol resulted in more incomplete hydrogenation with sterenes being generated, and in addition to 5α and 5β-cholestane, diasteranes were also generated via migration of the double bond.     

Recent advances in star-formation studies

David A Williams and Serena Viti survey the contributions made to this fast-moving field at a recent RAS Discussion Meeting. The resulting debates were often both challenging and confrontational.