Analysis of rock samples collected from rock hewn churches of Lalibela,Ethiopia using laser-induced breakdown spectroscopy

With the aim to study alteration processes of the rock hewn churches from Lalibela (Ethiopia), we applied Laser Induced Breakdown Spectroscopy (LIBS) technique to measure the elemental composition both of the bulk rock materials and their external layers, exposed to the environmental factors. The analytical plasma was generated by nanosecond pulses of an Nd: YAG laser emitting at 1064 nm. Different major and minor sample constituents were detected, including Ca, Mg, Na, Fe, Ti, Al and K. The detected O emission originates both from air surrounding and the sample, while the intensity of N lines, coming exclusively from air, was used for the LIBS signal normalization. By depth profiling of the weathered basalt rock, we observed a lower presence of K in the external layers, corresponding to the first 5 laser shots. The emission from this element is anti-correlated with the line intensities from O, and this was attributed to the variations in relative abundances of clay minerals and K-feldspar. The analogue measurements were performed on the tuff rock, and compared to the spectra from powder samples containing only the external soft material, scratched from the rocks. These analyses show an abundance of H in the weathered, wetted layers and suggest that cations are lost from the constituent primary minerals and replaced by H⁺; this process disrupts the lattice structure and causes a marked loss of strength. The studies presented here demonstrate that LIBS is a useful technique for studying the alteration processes in the rocks, caused by environmental factors.     

Stable isotope analysis on human remains from the final Early Holocene in the southern Puna of Argentina: The case of Peñas de las Trampas 1.1

In this work are presented the results of isotopic analyses made on bone remains of human individuals (n?=?6) from the southern Puna of Argentina dated to the final Early Holocene (ca. 8230–8000 BP). They were found in structures located in Peñas de las Trampas 1.1, a rockshelter at 3582 m.a.s.l. in Antofagasta de la Sierra, in the southern Argentinian Puna. They contain multiple secondary burials. Bone fragments were recovered from at least six individuals, three in each structure. Stable isotopes of Carbon (δ¹³C) and Nitrogen (δ¹⁵N) analysis were aimed at defining aspects related to the palaeodiet of the six individuals within the palaeo-economic subsistence spectrum typical of hunter–gatherers. It is worth noting that these human remains are among the earliest from North-Western Argentina, where funeral practices are related with the transportation of certain anatomical parts. The palaeodietary inference considers, on the one hand, the extreme aridity of this geographical area and its impact on the isotopic ecology. And, on the other, it takes into account the fact that four of the six individuals under study were breastfed infants. The results are in agreement with the expected values of the period, which has been characterized as the beginning of the arid Altithermal.     

Arch Dam-Fluid Interaction Considering Reservoir Topology

The magnitudes of the hydrodynamic pressures at the dam-fluid interface depend on the amount of energy transmitted to the fluid by the vibration of the reservoir boundaries. Although the reservoir topology can have a considerable impact on the amount of generated energy, it has still not been adequately addressed. This article treats an arch dam-fluid interaction considering a compound wave field of compressive and dilatational waves in a reservoir with a complex topology. A truncation surface was located at a distance beyond which the simulated wave field has only negligible effects.