Authors:M. Lemańska, J. Rodríguez-Velázquez and I. Gonzalez Yero
The distance dG(u, v) between two vertices u and v in a connected graph G is the length of the shortest uv-path in G. A uv-path of length dG(u, v) is called a uv-geodesic. A set X is convex in G if vertices from all ab-geodesics belong to X for any two vertices a, b ∈ X. The convex domination number γcon(G) of a graph G equals the minimum cardinality of a convex dominating set. In the paper, Nordhaus-Gaddum-type results for the convex domination
number are studied.
Authors:V. Rodríguez-Lugo, L. Ortiz-Velázquez, J. Miranda, M. Ortiz-Rojas and V. Castaño
The characterization of samples of painted plasters obtained from the archaeological site of Xochicalco, in Central Mexico,
is presented. Elemental concentrations of the painted layers were obtained by using proton induced X-ray emission (PIXE).
The main crystalline structures of the samples are identified with the help of X-ray diffraction (XRD), while the microstructure
is studied by scanning electron microscopy (SEM). The information resulting from the application of these three techniques
is used to achieve more accurate values for the elemental concentrations. Additional data regarding organic components of
the paintings was obtained through Fourier transform infrared spectrometry (FTIR). Although the latter results only provided
reliable data on inorganic components, they help to clarify the results from XRD and confirm those of SEM.