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Cuenca-Gotor V.P.,Polytechnic University of Valencia | Sans J.A.,Polytechnic University of Valencia | Ibanez J.,ICTJA CSIC | Popescu C.,ALBA Synchrotron Light Facility | And 12 more authors.
Journal of Physical Chemistry C | Year: 2016

We report a study of the structural, vibrational, and electronic properties of layered monoclinic arsenic telluride (α-As2Te3) at high pressures. Powder X-ray diffraction and Raman scattering measurements up to 17 GPa have been complemented with ab initio total-energy, lattice dynamics, and electronic band structure calculations. Our measurements, which include previously unreported Raman scattering measurements for crystalline α-As2Te3, show that this compound undergoes a reversible phase transition above 14 GPa at room temperature. The monoclinic crystalline structure of α-As2Te3 and its behavior under compression are analyzed by means of the compressibility tensor. Major structural and vibrational changes are observed in the range between 2 and 4 GPa and can be ascribed to the strengthening of interlayer bonds. No evidence of any isostructural phase transition has been observed in α-As2Te3. A comparison with other group 15 sesquichalcogenides allows understanding the structure of α-As2Te3 and its behavior under compression based on the activity of the cation lone electron pair in these compounds. Finally, our electronic band structure calculations show that α-As2Te3 is a semiconductor at 1 atm, which undergoes a trivial semiconducting-metal transition above 4 GPa. The absence of a pressure-induced electronic topological transition in α-As2Te3 is discussed. © 2016 American Chemical Society.

Ricci T.,Italian National Institute of Geophysics and Volcanology | Finizola A.,University of Reunion Island | Barde-Cabusson S.,ICTJA CSIC | Delcher E.,University of Reunion Island | And 3 more authors.
Geology | Year: 2015

Detecting volcanic unrest is of primary importance for eruption forecasting, especially on volcanoes characterized by highly dangerous, and often seemingly unpredictable, phreatic or phreatomagmatic eruptions. We present a simple and innovative analysis of shallow vertical temperature profiles to depths of 70 cm. These data were recorded at La Fossa cone of Vulcano (Aeolian Islands, Italy), during an episode of increased hydrothermal and seismic activities that occurred between September and December 2009. This work involves the use of the coefficient of determination (R2) on vertical temperature profiles in order to identify changes in conductive versus convective heat transfer modality. The increase in convective heat transfer can be related to the disruption of the hydrothermal system due to its pressurization and/or variation of ground permeability between the hydrothermal system and the surface. While raw temperature data do not evidence any significant variation during the period investigated and the classic temperature gradient is highly influenced by seasonal variations, the fluctuation of R2 displayed striking spikes that coincided with the seismic swarm inside the volcanic edifice. Such a low-cost device associated with easy real-time data processing could constitute a very promising, yet deceptively simple, technique to monitor hydrothermal systems, in order to assess the hazard posed by high-energy eruptions for populations living close to active volcanoes. © 2015 Geological Society of America.

Freire C.,University of Granada | Ramos R.,University of Granada | Lopez-Espinosa M.-J.,University of Granada | Lopez-Espinosa M.-J.,Center for Public Health Research | And 5 more authors.
Environmental Research | Year: 2010

The main source of human exposure to mercury is the consumption of fish contaminated with methylmercury, which may adversely affect early neurodevelopment. This study assessed mercury levels in hair of preschoolers in Spain, where fish consumption is elevated, with the aim of investigating the influence of their fish intake and other factors on mercury exposure, and evaluating their association with cognitive development. A population-based birth cohort from Granada (Spain) was studied at the age of 4 yr. Total mercury (T-Hg) levels were determined in children's hair, and daily fish intake was assessed by a food frequency questionnaire. The McCarthy Scales of Children's Abilities (MSCA) were used to assess children's motor and cognitive abilities. Complete data were gathered on 72 children, and multivariate analyses were performed to evaluate the influence of mercury exposure and fish intake on MSCA outcomes. Mean concentration of T-Hg in hair was 0.96 μg/g (95% confidence interval=0.76; 1.20 μg/g). T-Hg levels were associated with higher frequency of oily fish consumption, place of residence, maternal age, and passive smoking. After adjustment for fish intake, T-Hg levels ≥1 μg/g were associated with decrements in the general cognitive (-6.6 points), memory (-8.4 points), and verbal (-7.5 points) MSCA scores. Higher mercury exposure in children from this Mediterranean area was associated with cognitive development delay. Studies on the putative benefits of fish intake during early development should consider mercury exposure from different fish species. © 2009 Elsevier Inc. All rights reserved.

Diaz J.,ICTJA CSIC | Gallart J.,ICTJA CSIC | Morais I.,Instituto Dom Luiz IDL | Silveira G.,Instituto Dom Luiz IDL | And 7 more authors.
Tectonophysics | Year: 2015

The knowledge of the anisotropic properties beneath the Iberian Peninsula and Northern Morocco has been dramatically improved since late 2007 with the analysis of the data provided by the dense TopoIberia broad-band seismic network, the increasing number of permanent stations operating in Morocco, Portugal and Spain, and the contribution of smaller scale/higher resolution experiments. Results from the two first TopoIberia deployments have evidenced a spectacular rotation of the fast polarization direction (FPD) along the Gibraltar Arc, interpreted as an evidence of mantle flow deflected around the high velocity slab beneath the Alboran Sea, and a rather uniform N100°E FPD beneath the central Iberian Variscan Massif, consistent with global mantle flow models taking into account contributions of surface plate motion, density variations and net lithosphere rotation. The results from the last Iberarray deployment presented here, covering the northern part of the Iberian Peninsula, also show a rather uniform FPD orientation close to N100°E, thus confirming the previous interpretation globally relating the anisotropic parameters to the LPO of mantle minerals generated by mantle flow at asthenospheric depths. However, the degree of anisotropy varies significantly, from delay time values of around 0.5 s beneath NW Iberia to values reaching 2.0 s in its NE corner. The anisotropic parameters retrieved from single events providing high quality data also show significant differences for stations located in the Variscan units of NW Iberia, suggesting that the region includes multiple anisotropic layers or complex anisotropy systems. These results allow to complete the map of the anisotropic properties of the westernmost Mediterranean region, which can now be considered as one of best constrained regions worldwide, with more than 300 sites investigated over an area extending from the Bay of Biscay to the Sahara platform. © 2015 Elsevier B.V.

Earth-Science Reviews | Year: 2016

The increasing number of broad-band seismic stations recording the full spectrum of the seismic wavefield continuously has boosted interest in background signals recorded in the absence of earthquakes. Different human-made and natural phenomena other than earthquakes result in Earth vibrations that are recorded on seismometers. Those signals have classically been considered as disturbing noise, but in the last decades this view has turned, as it has been shown that seismic data can be used not only to monitor earthquake activity, but also to investigate climatic changes, track hurricanes, monitor river flows, or survey anthropogenic activity, hence making new links between seismology and different research fields. This contribution reviews state-of-the-art knowledge on the sources of seismic energy in different frequency bands using a single, two-weeks-long, seismic data file recorded by a high quality broad-band station located in the Pyrenees. This data allows exploration of the wide spectrum of ground motion, enabling a review of different processes involved in the generation of what seismologists commonly regard as background noise when focusing on ground motion from local and teleseismic earthquakes and explosions recorded in the same time interval. © 2016 Elsevier B.V.

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