We test the validity of gold−hydrogen analogy in a hydrogen-atom-doped larger gold cluster, namely, Au 20 , which has attracted considerable interest in recent years because of its unique nature. For this purpose, we carry out density functional theory based calculations to determine the structures of various possible isomers of Au 19 H cluster by employing GGA and meta-GGA functionals. To obtain the optimized structures of Au 19 H cluster, several possible initial geometries have been explored. We find that the structure of Au 19 H cluster is very close to that of tetrahedral Au 20 cluster, and the dopant H atom prefers to sit on one of the vertices of the tetrahedron. On the other hand, for the cases of Li, coinage metal (Cu and Ag), and Pt atom doping, the dopant atom has been shown to preferably sit on the surface site of the tetrahedral Au 20 cluster. The structure and HOMO−LUMO gap of the Au 19 H cluster are found to be very close to that of the pure Au 20 cluster. Moreover, we observe that the adsorption energies and the extent of activations of CO and O 2 molecules on Au 19 H cluster are similar to those on the Au 20 cluster. On the other hand, it has been reported in the literature that in the smaller sized gold clusters the catalytic activity of the clusters is found to be enhanced significantly due to the doping with a hydrogen atom. Hence, it is clear from the present study that the structure and the electronic properties of hydrogen-atom-doped 20-atom gold cluster almost remain the same as that of Au 20 cluster, thereby demonstrating the existence of gold−hydrogen analogy in a larger sized gold cluster.

No abstract

Geologists and undergraduate students observed eight artificial "rock outcrops" in a realistically scaled field area, and then tried to envision a geological structure that might plausibly be formed by the layered rocks in the set of outcrops. Students were videotaped as they selected which of fourteen 3-D models they thought best represented the geological structure and then explained their choice. The focus of this paper is on how students reasoned from observations to inferences. Students used observations of outcrops' location, steepness (dip), orientation (strike), stratigraphy, and placement relative to topography to infer whether the structure was convex or concave, deep or shallow, symmetrical or asymmetrical, open or closed, and elongate or circular. On average, science majors produced more than twice as many evidence-supported claims than did non-science majors. Science majors produced more valid lines of reasoning than did non-science majors, and students who selected a correct model produced more valid lines of reasoning than students who selected an erroneous model. Apparent challenges included identifying appropriate observational evidence, combining multiple lines of reasoning, and understanding the scale relationship between candidate models and the full-scale structure.

No abstract