Ab initio quantum mechanical study of γ-AlOOH boehmite: structure and vibrational spectrum

The structure and vibrational spectrum of boehmite have been investigated at the quantum-mechanical level with the CRYSTAL code, using a Gaussian-type basis set and the B3LYP Hamiltonian. Three space groups are considered in this study: Cmcm, Cmc2₁, P2₁/c. Cmcm turns out to correspond to a transition state, whereas Cmc2₁ and P2₁/c are minimum energy structures. The difference among them is the position of H atoms only, the Al-O frame being essentially the same. Harmonic frequencies at the Γ point have been computed. The comparison between calculated and experimental frequencies shows a good agreement for the Al-O part of the spectrum (under 790 cm⁻¹). For the Al-OH bending modes (800–1,300 cm⁻¹) an absolute differences of 50–100 cm⁻¹ is observed; for the OH stretching modes (3,200–3,500 cm⁻¹) it increases to 120–200 cm⁻¹: anharmonicity is large because OH groups are involved in strong hydrogen bonds.     

An expanding Universe with constant pressure and no cosmological constant

Thanks to its fitting triumph, the ΛCDM paradigm is assumed to be the most powerful model, for describing the Universe dynamics, over much the myriad of cosmological models. Unfortunately, the quest of a self-consistent model remains not well explained, because it is not clear how to solve the problems of fine-tuning and coincidence, afflicting the ΛCDM framework; as a matter of fact, these theoretical drawbacks do not allow to consider the ΛCDM model, as the final picture of the modern cosmological scenario. Here, we show that the simplest model, which provides a constant equation of state for the pressure, leads to a generalization of ΛCDM, reducing to it in a particular case. Moreover, we highlight the physical mechanisms of this model, describing the thermodynamical reasons why a constant pressure should be negative in an expanding Universe. In addition, we fit the free parameters of our model by minimizing the chi square through the age differential method, involving a direct measurement of H.     

Snow cover monitoring in the Northern Patagonia Icefield using MODIS satellite images (2000–2006)

The snow cover of the Northern Patagonia Icefield (NPI) was monitored after applying the Normalized Difference Snow Index (NDSI) and the Red/NIR band ratio to 134 Moderate Resolution Imaging Spectroradiometer (MODIS) images captured between 2000 and 2006. The final results show that the snow cover extent of the NPI fluctuates a lot in winter, in addition to its seasonal behaviour. The minimum snow cover extent of the period (3600 km²) was observed in March 2000 and the maximum (11,623 km²) in August 2001. We found that temperature accounts for approximately 76% of the variation of the snow cover extent over the entire icefield. We also show two different regimes of winter snow cover fluctuations corresponding to the eastern and the western sides of the icefield. The seasonality of the snow cover on the western side was determined by temperature rather than precipitation, while on the east side the seasonality of the snow cover was influenced by the seasonal behaviour of both temperature and precipitation. This difference can be explained by the two distinct climates: coastal and continental. The fluctuations in the winter snow cover extent were more pronounced and less controlled by temperature on the western side than on the eastern side of the icefield. Snow cover extent was correlated with temperature R² = 0.75 and R² = 0.74 for the western and eastern sides, respectively. Since limited meteorological data are available in this region, our investigation confirmed that the change in snow cover is an interesting climatic indicator over the NPI providing important insights in mass balance comprehension. Since snow and ice were distinguished snow cover fluctuations can be associated to fluctuations in the snow accumulation area of the NPI. In addition, days with minimum snow covers of summer season can be associated to the period in which Equilibrium Line Altitude (ELA) is the highest.     

Mantle source heterogeneity in subduction zones: constraints from elemental and isotope (Sr,Nd, and Pb) data on Vulcano Island,Aeolian Archipelago,Italy

Mineralogy and Petrology - Vulcano is part of the Aeolian volcanic arc in the southern Tyrrhenian Sea. Its products were emplaced through multiple episodes of edifice building and collapse since...     

Spatial coherency analysis of seismic ground motions from a rock site dense array implemented during the Kefalonia 2014 aftershock sequence

The objective of studies presented in this paper is to analyse the spatial incoherency of seismic ground motions using signals from a velocimeter dense array located on a rock site, recording the aftershock sequence of the two M6 Kefalonia earthquakes that occurred in January/February 2014 (Kefalonia island, Greece). The analyses are carried out with both horizontal and vertical components of velocigrams for small separation distances of stations (<100 m). The coherencies of seismic ground motions identified from strong motion windows are compared with those identified from coda parts of signals. It is realized that there is no significant difference between the coherencies estimated from those two parts of signals. The influence of earthquake event number on the result of coherencies and the dispersions of coherencies estimated from different earthquake events are presented. Finally, coherencies estimated from the dense array are compared with several coherency models proposed and widely used in the literature. The possibility of modifying some parameters of those existing coherency models to fit with in situ coherencies are discussed and presented. Copyright © 2017 John Wiley & Sons, Ltd.     

Non-invasive lab test in the monitoring of vadose zone contaminated by light non-aqueous phase liquid

We discuss a strategy capable of a quantitative long-term monitoring of water saturation and volume variation of light non-aqueous phase liquids in the soil. The goal was reached monitoring a controlled sand cell contaminated with classical gasoline over 124 days, using geophysical methods such as electrical resistivity tomography, induced polarization and ground penetrating radar. We show that empirical relations, linking the water saturation to the physical parameters measured as resistivity from electrical resistivity tomography and travel time from georadar with advanced processing, are good tools for this purpose. The consistence of the proposed process is validated by both good overlap of results carried out from electrical resistivity tomography and georadar and theoretical models simulating the actual experiment.     

Late‐glacial and Holocene history of the dry forest area in the south Colombian Cauca Valley

Two sedimentary cores with pollen, charcoal and radiocarbon data are presented. These records document the Late‐glacial and Holocene dry forest vegetation, fire and environmental history of the southern Cauca Valley in Colombia (1020 m). Core Quilichao‐1 (640 cm; 3° 6′N, 76° 31′W) represents the periods of 13 150–7720 ¹⁴C yr BP and, following a hiatus, from 2880 ¹⁴C yr BP to modern. Core La Teta‐2 (250 cm; 3° 5′N, 76° 32′W) provides a continuous record from 8700 ¹⁴C yr BP to modern. Around 13 150 ¹⁴C yr BP core Quilichao‐1 shows an active Late‐glacial drainage system and presence of dry forest. From 11 465 to 10 520 ¹⁴C yr BP dry forest consists mainly of Crotalaria, Moraceae/Urticaceae, Melastomataceae/Combretaceae, Piper and low stature trees, such as Acalypha, Alchornea, Cecropia and Celtis. At higher elevation Andean forest comprising Alnus, Hedyosmum, Quercus and Myrica was common. After 10 520 ¹⁴C yr BP the floral composition of dry forest changed, with extensive open grass vegetation indicative of dry climatic conditions. This event may coincide with the change to cool and dry conditions in the second part of the El Abra stadial, an equivalent to the Younger Dryas. From 8850 ¹⁴C yr BP the record from La Teta indicates dry climatic conditions relative to the present, these prevailing up to 2880 ¹⁴C yr BP at Quilichao and to 2720 ¹⁴C yr BP at La Teta. Severe dryness reached maxima at 7500 ¹⁴C yr BP and 4300 ¹⁴C yr BP, when dry forest reached maximum expansion. Dry forest was gradually replaced by grassy vegetation, reaching maximum expansion around 2300 ¹⁴C yr BP. After 2300 ¹⁴C yr BP grassy vegetation remains abundant. Presence of crop taxa (a.o. Zea mays), disturbance indicators (Cecropia) and an increase in charcoal point to the presence of pre‐Columbian people since 2300 ¹⁴C yr BP. After 950 ¹⁴C yr BP, expansion of secondary forest taxa may indicate depopulation and abandonment of previously cultivated land. After 400 ¹⁴C yr BP, possibly related to the Spanish conquest, secondary forest expanded and charcoal concentrations increased, possibly indicating further reduction of cultivated land. During the past century, Heliotropium and Didymopanax became abundant in an increasingly degraded landscape. Copyright © 2002 John Wiley & Sons, Ltd.     

Kinematic interaction factors of deep foundations with inclined piles

The beneficial or detrimental role of battered piles on the dynamic response of piled foundations has not been yet fully elucidated. In order to shed more light on this aspect, kinematic interaction factors of deep foundations with inclined piles, are provided for single‐battered piles, as well as for 2 × 2 and 3 × 3 groups of piles subjected to vertically incident plane shear S waves. Piles are modelled as linear‐elastic Bernoulli beams, whereas soil is assumed to be a linear, isotropic, homogeneous viscoelastic half‐space. Different pile group configurations, pile‐soil stiffness ratios, and rake angles are considered. The relevance and main trends observed in the influence of the rake angle on the kinematic interaction factors of the analysed foundations are inferred from the presented results. An important dependence of the kinematic interaction factors on the rake angle is observed together with the existence of an inclination angle at which cap rotation and excitation become out of phase in the low‐to‐mid frequency range. The existence of a small batter angle that provides minimum cap rotation is also shown. Copyright © 2014 John Wiley & Sons, Ltd.     

A note on smoothness measures for space–time surfaces

The differentiability of a random field has a direct relationship with the differentiability of its covariance function. We review the concept of differentiability of space–time covariance models and random fields, and its implications on predictions. We analyze the change of behavior of the covariance function at the origin and at different space–time lags away from the origin, by using the concept of smoothness which can be considered the geometrical view of the differentiability. We propose a way to measure the smoothness of any covariance function, and apply it to purely spatial and space–time covariance functions.