Nanoparticles of platinum-group metals (PGM) on carbon supports are widely used as catalysts for a number of chemical and electrochemical conversions on laboratory and industrial scale. The newly emerging field of single atom catalysis focuses on the ultimate level of metal dispersion, i.e. atomically dispersed metal species anchored on the substrate surface. However, the presence of single atoms in traditional nanoparticle-based catalysts remains largely overlooked. In this work we use aberration-corrected scanning transmission electron microscope to investigate four commercially available nanoparticle-based PGM/C catalysts (PGM = Ru, Rh, Pd, Pt). We show that in addition to nanoparticles, single atoms are also present on the surface of carbon substrates. These observations raise questions about the role that single atoms play in conventional nanoparticle PGM/C catalysts. We critically discuss the observations with regard to the quickly developing field of single atom catalysis.

The aim of this study was to determine the relationship between levels of leisure-time sports and physical activity and the stages of change in high school students with goal orientations. Methods: The sample consisted of 2168 students randomly selected to participate in a longitudinal study in Costa Rica (423), Mexico (408) and Spain (1337), with 1052 being boys, 1037 girls and 79 who did not specify sex, aged between 11 and 16 years old (M = 12.49, SD = .81). We used a questionnaire to ask students about their leisure-time sports and physical activity, about stages of change and to measure achievement goals. Results: The results show that students are more active in Costa Rica, most of them being in the stage of active change. Conclusions: We found significant differences in achievement goals in all three countries, which shows that students in active stages have higher values than those in the inactive stage.

In this work, some micro-samples belonging to the open-air rock art site of Cueva de la Vieja (Alpera, Albacete, Spain) were analysed. These samples were collected after and before a desalination treatment carried out with the aim of removing a whitish layer of concretion that affected the painted panel. The diagnostic study was performed to study the conservation state of the panel and then to confirm the effectiveness of treatment. Micro energy dispersive X-ray fluorescence spectrometry, Raman spectroscopy and X-ray diffraction were employed for the characterization of the degradation product as well as that of mineral substrate and pigments. The micro-samples analysis demonstrated that the painted layer was settled on a dolomitic limestone with silicon aggregates and aluminosilicates as well as iron oxides. The whitish crust was composed by sulfate compounds like gypsum (CaSO4·2H2O) with minor amount of epsomite (MgSO4.7H2O). An extensive phenomenon of biological activity was demonstrated since, in almost all the samples analysed, the presence of calcium oxalates monohydrate (CaC2O4H2O) and dehydrate (CaC2O42H2O) were found. Probably the presence of both calcium oxalates had favoured the conservation of pictographs. In addition, some carotenoids pigments, scytonemin (C36H20N2O4) and astaxanthin (C40H52O4) were characterized both by Raman spectroscopy and by X-ray diffraction. Hematite was found as a pigment voluntarily used for the painting of the panels used in mix with hydroxyapatite and amorphous carbon. The results of the analyses of the samples taken after the cleaning treatment confirmed a substantial decrease in sulphate patina on the panel surface.

Estuaries are excellent environments of identifying pollution episodes that have affected river basins, as their sediments are the final destination of some of the pollutants. This paper studies the geochemical evolution of five elements (As, Co, Cu, Pb, Zn) in a core extracted from the middle estuary of the Tinto River (SW Spain). Results are based on facies interpretation, ICP Atomic Emission Spectrometry analysis, the application of a regional background to obtain the geoaccumulation index and dating. Four pollution episodes have been detected at ~5.8 cal. kyr BP (acid mine drainage?), 4.7-4.5 kyr BP (first mining activities), the 1850-1960 interval (intensive mining) and the second half of the 20th century (intensive mining and industrial inputs). All episodes show an increase in one or more of these elements, as well as changes in their geochemical classes deduced from the geoaccumulation index.