Calculating glass-forming ability in absence of key kinetic and thermodynamic parameters

Glass-forming ability (GFA) as defined by a critical cooling rate R_c to vitrify a liquid upon solidification is a complex function of many parameters. Some of the parameters, such as liquid-crystal interfacial energy, temperature-dependent liquid viscosity, and influence of heterogeneities, are crucial but their accurate experimental determination is challenging. Here, instead of relying on the experimental data, we draw random values for the difficult parameters and use the classical theory to examine probabilistic distributions of Rc for two well-known metallic glasses. Direct random parameterization produces extremely broad distributions spanning tens of orders of magnitude. Dramatically sharpened distributions are obtained around experimental R_c upon guiding the random parameterization with limited calorimetric data. The results suggest that it is plausible to determine GFA even in absence of data for crucial parameters

The Type Ic Supernova 1994I in M51: Detection of Helium and Spectral Evolution

We present a series of spectra of SN 1994I in M51, starting 1 week prior to maximum brightness. The nebular phase began about 2 months after the explosion; together with the rapid decline of the optical light, this suggests that the ejected mass was small. Although lines of He I in the optical region are weak or absent, consistent with the Type Ic classification, we detect strong He I λ10830 absorption during the first month past maximum. Thus, if SN 1994I is a typical Type Ic supernova, the atmospheres of these objects cannot be completely devoid of helium. The emission-line widths are smaller than predicted by the model of Nomoto and coworkers, in which the iron core of a low-mass carbon-oxygen star collapses. They are, however, larger than in Type Ib supernovae