The electric field gradient in synthetic fayalite α-Fe2SiO4 at moderate temperatures

This work reports on the evaluation of the electric field gradient (efg) in synthetic fayalite α-Fe₂SiO₄ using three different procedures: (1) experimental, with single-crystal Mössbauer spectroscopy (SCMBS) on the three principal sections of an α-Fe₂SiO₄ sample for several temperatures in the range 20?°C?≤?T?≤?300?°C; (2) semiquantitative, with the on-line calculation of the efg from three-dimensional difference electron densities, and (3) a fully quantitative method with cluster molecular orbital calculations based on the density functional theory. The experimental efg is in good agreement with our previously published low-temperature data as well as with the results obtained by the fully quantitative approach. In the latter case, large cluster sizes (up to 97 atoms) are necessary to obtain quantitative agreement with experiment. This is also considered as being responsible for the lack of correspondence with the semiquantitative efg on M1. Previously reported symmetry violations on the M2 site are also confirmed by our SCMBS measurements.     

Reconstructing Phreatic Palaeogroundwater Levels in a Geoarchaeological Context: A Case Study in Flanders,Belgium

The complex debate on prehistoric settlement decisions is no longer tackled from a purely archaeological perspective but from a more landscape‐oriented manner combined with archaeological evidence. Therefore, reconstruction of several components of the former landscape is needed. Here, we focus on the reconstruction of the groundwater table based on modeling. The depth of the phreatic aquifer influences, for example, soil formation processes and vegetation type. Furthermore, it directly influences settlement by the wetness of a site. Palaeogroundwater modeling of the phreatic aquifer was carried out to produce a series of full‐coverage maps of the mean water table depth between 12.7 ka and the middle of the 20th century (1953) in Flanders, Belgium. The research focuses on the reconstruction of the input data and boundary conditions of the model and the model calibration. The model was calibrated for the 1924–1953 time period using drainage class maps. Archaeological site data and podzol occurrence data act as proxies for local drainage conditions over periods in the past. They also served as a control on the simulated phreatic palaeogroundwater levels. Model quality testing on an independent validation data set showed that the model predicts phreatic water table levels at the time of soil mapping well (mean error of 1.8 cm; root mean square error of 65.6 cm). Simulated hydrological conditions were in agreement with the occurrence of archaeological sites of Mesolithic to Roman age at 96% of the validation locations, and also with the occurrence of well‐drained podzols at 97% of the validation locations.     

Uncertainty in Carbon Capture and Storage (CCS) deployment projections: a cross-model comparison exercise

Carbon Capture and Storage (CCS) can be a valuable CO₂ mitigation option, but what role CCS will play in the future is uncertain. In this paper we analyze the results of different integrated assessment models (IAMs) taking part in the 27th round of the Energy Modeling Forum (EMF) with respect to the role of CCS in long term mitigation scenarios. Specifically we look into the use of CCS as a function of time, mitigation targets, availability of renewables and its use with different fuels. Furthermore, we explore the possibility to relate model results to general and CCS specific model assumptions. The results show a wide range of cumulative capture in the 2010–2100 period (600–3050 GtCO₂), but the fact that no model projects less than 600 GtCO₂ indicates that CCS is considered to be important by all these models. Interestingly, CCS storage rates are often projected to be still increasing in the second half of this century. Depending on the scenario, at least six out of eight, up to all models show higher storage rates in 2100 than in 2050. CCS shares in cumulative primary energy use are in most models increasing with the stringency of the target or under conservative availability of renewables. The strong variations of CCS deployment projection rates could not be related to the reported differences in the assumptions of the models by means of a cross-model comparison in this sample.