Search results for " Petr"
showing 10 items of 1574 documents
Field-portable Mössbauer spectroscopy on Earth, the Moon, Mars, and beyond
2011
ABSTRACT Iron occurs naturally as Fe 2+ , Fe 3+ , and, to a lesser extent, as Fe 0 . Many fundamental (bio)geochemical processes are based on redox cycling between these oxidation states. Mossbauer spectroscopy provides quantitative information about the distribution of Fe among its oxidation states, identification of Fe-bearing phases, and relative distribution of Fe among those phases. Portable, miniaturised Mossbauer spectrometers were developed for NASA9s Mars Exploration Rovers (in operation since 2004) and provide a means for non-destructive, in-situ field investigations. On Mars, these instruments provided evidence for aqueous activity with implications for habitability, were applied…
Garnet and spinel lherzolite assemblages in MgO-Al2O3-SiO2 and CaO-MgO-Al2O3-SiO2: thermodynamic models and an experimental conflict
2012
The recent publication of an updated thermodynamic dataset for petrological calculations provides an opportunity to illustrate the relationship between experimental data and the dataset, in the context of a new set of activity–composition models for several key minerals. These models represent orthopyroxene, clinopyroxene and garnet in the system CaO–MgO–Al2O3–SiO2 (CMAS), and are valid up to 50 kbar and at least 1800 °C; they are the first high-temperature models for these phases to be developed for the Holland & Powell dataset. The models are calibrated with reference to phase-relation data in the subsystems CaO–MgO–SiO2 (CMS) and MgO–Al2O3–SiO2 (MAS), and will themselves form the basis o…
Short-term response to waterlogging in Quercus petraea and Quercus robur: A study of the root hydraulic responses and the transcriptional pattern of …
2015
International audience; We characterized the short-term response to waterlogging in Quercus petraea (Matt.) Liebl. and Quercus robur L. as the initial response towards their known long-term differences in tolerance to waterlogging. One-month old seedlings were subjected to hypoxic stress and leaf gas exchange, shoot water potential (Psi(s)) and root hydraulic conductivity (Lp(r)) were measured. In parallel, the expression of nine aquaporins (AQPs) along the primary root was analysed by quantitative RT-PCR. Results showed a similar reduction in net assimilation (A) and stomatal conductance (g(s)) for the two species. Notably, the response of Lpr differed temporally between the two species. Q…
Managing soil nitrate with cover crops and buffer strips in Sicilian vineyards
2013
When soil nitrate levels are low, plants suffer nitrogen (N) deficiency but when the levels are excessive, soil nitrates can pollute surface and subsurface waters. Strategies to reduce the nitrate pollution are necessary to reach a sustainable use of resources such as soil, water and plant. Buffer strips and cover crops can contribute to the management of soil nitrates, but little is known of their effectiveness in semiarid vineyards plantations. The research was carried out in the south coast of Sicily (Italy) to evaluate nitrate trends in a vineyard managed both conventionally and using two different cover crops (Triticum durum and Vicia sativa cover crop). A 10 m-wide buffer strip was se…
The structure of reactive grain-boundaries under stress containing confined fluids
2006
We present numerical experiments on structure development in grain-boundaries during dissolution–precipitation creep. Two solids that are represented by an elastic spring configuration are pressed together with a compressible fluid in the grain-boundary. The solid can dissolve or precipitate depending on elastic and surface energy as well as fluid pressure and concentration of dissolved material in the fluid. We perform a number of numerical experiments with different starting configurations that represent a large-scale island-channel interface with solid–solid contacts across the islands, a rough grain-boundary interface with a fluid along the whole interface and a smooth thin-film interfa…
Microstructural, chemical and textural records during growth of snowball garnet
2009
The growth history of two populations of snowball garnet from the Lukmanier Pass area (central Swiss Alps) was examined through a detailed analysis of three-dimensional geometry, chemical zoning and crystallographic orientation. The first population, collected in the hinge of a chevron-type fold, shows an apparent rotation of 360 degrees. The first 270 degrees are characterized by spiral-shaped inclusion trails, gradual and concentric Mn zoning and a single crystallographic orientation, whereas in the last 90 degrees, crenulated inclusion trails and secondary Mn maxima centred on distinct crystallographic garnet domains are observed. Microstructural, geochemical and textural data indicate a…
Minute co-variations of Sr/Ca ratios and microstructures in the aragonitic shell of Cerastoderma edule (Bivalvia) – Are geochemical variations at the…
2017
Abstract It remains a challenging task to reconstruct water temperatures from Sr/Ca ratios of bivalve shells. Although in many aragonitic species, Sr/Ca is negatively correlated to temperature – which is expected based on abiogenic precipitation experiments, the incorporation of Sr into the shell of bivalves is strongly controlled by physiological processes and occurs away from the predicted thermodynamic equilibrium. Strontium-to-calcium ratios of aragonitic shells remain far below that of the ambient water. Moreover, Sr concentrations vary considerably among shell portions consisting of different microstructures and/or organic content. Values observed at annual growth lines and within the…
Helium–strontium isotope constraints on mantle evolution beneath the Roman Comagmatic Province, Italy
2004
- European Social Fund - Scottish Universities - Carnegie Trust for the Universities of Scotland.
Strontium and argon isotopic homogenization of pelitic sediments during low-grade regional metamorphism: The pan-African upper Damara sequence of Nor…
1979
Abstract The fine mineral fractions extracted from pelitic sediments of the Eocambrian upper Damaran Mulden Group were subjected to a detailed isotopic study by the Rb-Sr and K-Ar methods in combination with a mineralogical analysis by X-ray diffractometry. The sediments contain two major parageneses of metamorphic origin which can be related to two separate low-grade regional metamorphic events of anchizonal intensity with temperatures between 250 and 300°C and pressures up to 2 kbar. These events are dated at about 535 m.y. and 455 m.y. respectively (with λ( 87 Rb) = 1.42 × 10 −11 yr −1 ). Anomalously high K-Ar ages on samples from specific stratigraphic horizons can be related to open sy…
Recent advances in space-time statistics with applications to environmental data: An overview
2003
[1] This paper introduces a special section based on general environmental scientific problems, with a particular focus on using atmospheric data. All the papers and authors provide the methodology to study, analyze, predict, and evaluate the spatial-temporal behavior and the complicated spatial-temporal structure of the data. The overall aim is to present up-to-date developments in spatial and spatiotemporal statistics in the field of the atmosphere, to present on-going research, and to discuss important problems to be addressed in the near future.