RESUMO
White virgules, commas, and dot designs on tricolored ceramics are sporadically found in different archaeological sites located in Northwestern Argentina area, as Puna and Quebrada de Humahuaca. This decorating style has been reported in several articles, but few previous archaeometric studies have been carried out on the pigment composition. Fragments from Puna and Quebrada archaeological sites, belonging to Regional Development Period (900-1430 AD), were analyzed by X-ray diffraction and Raman spectroscopy in order to characterize the pigments employed. Red and black pigments are based on iron and manganese oxides, as it has been extensively reported for the NW Argentina area. White pigments from white virgules, comma, and dot designs have shown different composition. Hydroxyapatite was found in samples from Doncellas site (North Puna region), and calcium and calcium-magnesium containing compounds, as vaterite and dolomite, along with titanium containing compounds were detected on samples from Abralaite (Central Puna region) and Gasoducto (Quebrada de Humahuaca region). It has been concluded that pigment composition is not characteristic of a unique region.
RESUMO
The time dependent response of the magnetic and transport properties of Fe-doped phase separated (PS) manganite La(0.5)Ca(0.5)MnO3 is reported. The nontrivial coexistence of ferromagnetic (FM) and non-FM regions induces a slow dynamics which leads to time relaxation and cooling rate dependence within the PS regime. This dynamics influences physical properties drastically. On one hand, metalliclike behavior, assumed to be a fingerprint of percolation, can be also observed before the FM phase percolates as a result of dynamical contributions. On the other hand, two novel effects for the manganites are reported, namely, the rejuvenation of the resistivity after aging and a persistent memory of low magnetic fields (<1 T), imprinted in the amount of the FM phase.