ABSTRACT
Information on pigment sizes in mural samples is a key factor in determining the suitable processes of possible restoration and conservation on ancient murals and is also significant for the investigation of a mural's historic value and analysis of its technical process. Thus, in this paper, the green painted layers composed of different pigment sizes were analyzed by laser-induced breakdown spectroscopy. First, a parametric study was undertaken to optimize the LIBS signal to noise ratio and decrease fluctuations. Then, the variation of LIBS signal with pigment size was studied on simulated mural samples. Finally, a classifiable model of pigment sizes was built by coupling with the PCA method and was successfully applied to classify pigment sizes on real mural pieces.
ABSTRACT
The equilibrium structures, vibrational frequencies, and bond characteristics of NpO2(m+) ions and NpO2(H2O)n(m+) (m = 1-2, n = 1-6) complexes have been studied by carrying out ab initio calculations in the gas phase and aqueous solution. The geometries have been obtained at the B3LYP level with the use of the polarized continuum model (PCM). The computed structural parameters that are in reasonably good agreement with the available data show that the solvation effect leads to a red shift of the IR spectra and the weakness of interaction strengths in neptunyl ions. By comparing the structural properties and the density of states (DOS) of these aqua complexes in the gas phase and aqueous solution, it is found that the solvation effect can be simulated approximately with the calculations of these aqua complexes in the gas phase. In addition, the DOS of these aqua complexes together with the binding energies between the neptunyl ion and water molecule reveal that the penta-aqua complex is preferred for neptunyl ions in aqueous solution.