**Author details**

Miguel de Simón-Martín\*, Ana-María Diez-Suárez, Laura-Álvarez de Prado, Alberto González-Martínez, Álvaro de la Puente-Gil and Jorge Blanes-Peiró

\*Address all correspondence to: miguel.simon@unileon.es

Mines Engineering School, University of León, León, Spain
