Search results for "Thermal"
showing 10 items of 3576 documents
Isolation of the CH3˙ rotor in a thermally stable inert matrix: first characterization of the gradual transition from classical to quantum behaviour …
2014
International audience; Matrix isolation is a method which plays a key role in isolating and characterizing highly reactive molecularradicals. However, the isolation matrices, usually composed of noble gases or small diamagnetic molecules,are stable only at very low temperatures, as they begin to desegregate even above a few tens of Kelvin.Here we report on the successful isolation of CH3 radicals in the cages of a nearly inert clathrate–SiO2matrix. This host is found to exhibit a comparable inertness with respect to that of most conventionalnoble gas matrices but it is characterized by a peculiar thermal stability. The latter property is related to thecovalent nature of the host material a…
Geosphere-biosphere interactions in bio-activity volcanic lakes: Evidences from Hule and Rìo Cuarto (Costa Rica)
2014
Hule and R ́ıo Cuarto are maar lakes located 11 and 18 km N of Poa ́s volcano along a 27 km long fracture zone, in the Central Volcanic Range of Costa Rica. Both lakes are characterized by a stable thermic and chemical stratification and recently they were affected by fish killing events likely related to the uprising of deep anoxic waters to the surface caused by rollover phenomena. The vertical profiles of temperature, pH, redox potential, chemical and isotopic compositions of water and dissolved gases, as well as prokaryotic diversity estimated by DNA fingerprinting and massive 16S rRNA pyrosequencing along the water column of the two lakes, have highlighted that different bio-geochemica…
Rare earth elements and hydrothermal ore formation processes
1992
Abstract The geochemical behaviour of REE is influenced by nearly all important hydrothermal ore formation processes including fluid-rock interactions, fluid precipitations, adsorption and scavenging onto particles, and changes in fluid temperature, pressure, pH, Eh, alkalinity and ligand concentration. Destabilization of REE complexes in response to these physicochemical changes and possible chemical-crystallographic controls determine the concentration and distribution of REE within hydrothermal minerals, mineraloids and amorphous phases. Alteration assemblages of intrusive related mineralisations may exhibit a wide range of REE distributions and REE fractionation trends. The REE distribu…
Petrography and high-resolution geochemical records of Lower Jurassic manganese-rich deposits from Monte Mangart, Julian Alps
2016
Deposits with unusually high Mn contents sampled at Monte Mangart in the Julian Alps include organic-rich marlstone and black shale with interbedded manganoan and siliceous limestone, which were deposited during the early Toarcian Oceanic Anoxic Event. Mn enrichment during that period has been related to global sea-level change coincident with increasing subsidence rate. The formation of Fe-Mn nodules, marking a hardground at the base of the Monte Mangart section, seems to be triggered by release of Mn from remote hydrothermal vents into a region of relatively elevated submarine topography where oxidizing conditions prevailed. However, very high Mn contents in carbonate phases above the har…
Direct and fast determination of polychlorinated biphenyls in contaminated soils and sediments by thermal desorption-gas chromatography-tandem mass s…
2019
Abstract A direct procedure based on thermal desorption-gas chromatography-tandem mass spectrometry (TD–GC–MS–MS) was developed for the fast extraction of seven polychlorinated biphenyls (PCBs) from sediments and soils. PCBs were directly extracted, from 20 to 75 mg of sample, without any chemical pre-treatment or use of organic solvents, after the addition of 10 µL internal standard (PCB 195) in acetone. Sample treatment was totally automated. PCBs were extracted at 250 °C for 20 min, using a helium flow and the PCBs were trapped in a cryogenic Tenax trap at −10 °C. After that, analytes were directly desorbed at 270 °C and introduced to the GC–MS–MS system. Recoveries were established usin…
Turmoil at Turrialba Volcano (Costa Rica): Degassing and eruptive processes inferred from high-frequency gas monitoring.
2016
Abstract Eruptive activity at Turrialba Volcano (Costa Rica) has escalated significantly since 2014, causing airport and school closures in the capital city of San José. Whether or not new magma is involved in the current unrest seems probable but remains a matter of debate as ash deposits are dominated by hydrothermal material. Here we use high‐frequency gas monitoring to track the behavior of the volcano between 2014 and 2015 and to decipher magmatic versus hydrothermal contributions to the eruptions. Pulses of deeply derived CO2‐rich gas (CO2/Stotal > 4.5) precede explosive activity, providing a clear precursor to eruptive periods that occurs up to 2 weeks before eruptions, which are acc…
The structure of a hydrothermal system from an integrated geochemical, geophysical, and geological approach: The Ischia Island case study
2011
The complexity of volcano-hosted hydrothermal systems is such that thorough characterization requires extensive and interdisciplinary work. We use here an integrated multidisciplinary approach, combining geological investigations with hydrogeochemical and soil degassing prospecting, and resistivity surveys, to provide a comprehensive characterization of the shallow structure of the southwestern Ischia's hydrothermal system. We show that the investigated area is characterized by a structural setting that, although very complex, can be schematized in three sectors, namely, the extra caldera sector (ECS), caldera floor sector (CFS), and resurgent caldera sector (RCS). This contrasted structura…
So close, so different: geothermal flux shapes divergent soil microbial communities at neighbouring sites
2016
This study is focused on the (micro)biogeochemical features of two close geothermal sites (FAV1 and FAV2), both selected at the main exhalative area of Pantelleria Island, Italy. A previous biogeochemical survey revealed high CH4 consumption and the presence of a diverse community of methanotrophs at FAV2 site, whereas the close site FAV1 was apparently devoid of methanotrophs and recorded no CH4 consumption. Next-Generation Sequencing (NGS) techniques were applied to describe the bacterial and archaeal communities which have been linked to the physicochemical conditions and the geothermal sources of energy available at the two sites. Both sites are dominated by Bacteria and host a negligib…
Gaseous emissions from geothermal and volcanic areas: focus on methane and methanotrophs
2014
Ogni anno, 22 Tg di CH4 vengono rilasciati in atmosfera da numerose sorgenti sia naturali che antropiche. Il metano riveste un ruolo molto importante nella chimica dell’atmosfera terrestre e nel bilancio dell’energia radiante assorbita, essendo il secondo gas serra più potente dopo la CO2. Le aree vulcaniche e geotermali contribuiscono al flusso di metano in atmosfera, essendo vaste aree di degassamento. Studi preliminari hanno stimato che le emissioni globali di metano dai sistemi geotermali e vulcanici europei sono nel range di 4-16 kt a-1. Questa stima è stata ottenuta indirettamente dai dati delle emissioni di CO2 o H2O e dal rapporto del flusso CO2/CH4 oppure H2O/CH4 misurati nelle pri…