The helium abundance and ΔY/ΔZ in lower main-sequence stars

We use nearby K dwarf stars to measure the helium-to-metal enrichment ratio  Δ Y /Δ Z   , a diagnostic of the chemical history of the solar neighbourhood. Our sample of K dwarfs has homogeneously determined effective temperatures, bolometric luminosities and metallicities, allowing us to fit each star to the appropriate stellar isochrone and determine its helium content indirectly. We use a newly computed set of Padova isochrones which cover a wide range of helium and metal content.
Our theoretical isochrones have been checked against a congruous set of main-sequence binaries with accurately measured masses, to discuss and validate their range of applicability. We find that the stellar masses deduced from the isochrones are usually in excellent agreement with empirical measurements. Good agreement is also found with empirical mass-luminosity relations.
Despite fitting the masses of the stars very well, we find that anomalously low helium content (lower than primordial helium) is required to fit the luminosities and temperatures of the metal-poor K dwarfs, while more conventional values of the helium content are derived for the stars around solar metallicity.
We have investigated the effect of diffusion in stellar models and the assumption of local thermodynamic equilibrium (LTE) in deriving metallicities. Neither of these is able to resolve the low-helium problem alone and only marginally if the cumulated effects are included, unless we assume a mixing-length which is strongly decreasing with metallicity. Further work in stellar models is urgently needed.
The helium-to-metal enrichment ratio is found to be  Δ Y /Δ Z = 2.1 ± 0.9  around and above solar metallicity, consistent with previous studies, whereas open problems still remain at the lowest metallicities. Finally, we determine the helium content for a set of planetary host stars.     

Impact of past mining activity on the quality of groundwater in SW Sardinia (Italy)

Hydrogeochemical surveys were carried out in SW Sardinia (Italy) to investigate the impact of past mining activities on the quality of groundwater. The chemistry of waters from flooded galleries, adits and dumps has been compared with that of springs and wells in the same area at sites relatively far from any mine legacy. A feature, common to all waters, is the circumneutral pH, since the carbonate formations in the area neutralise the acidity produced by the oxidation of Fe-bearing sulphide minerals in the mine impacted water. However, groundwater interacting with mine workings is degraded in quality; it shows high dissolved SO₄, Zn, Cd and Pb contents. In some cases groundwater exceeds the limit established by the guidelines of the World Health Organization for Pb content in drinking water, so that groundwater is mixed before entering the local aqueducts. Results from this study suggest that more attention needs to be paid to the impact on the streams from contaminated water flowing out from some mine areas because during the dry season these streams are only fed by mine groundwater. We recommend focusing efforts to reduce the chemical contamination prior to discharge.     

Characterizing the vadose zone and a perched aquifer near the Vosges ridge at the La Soutte experimental site,Obernai, France

We consider a series of hydrogeophysical techniques that provide a multiscale investigation of the water content in the vadose zone and of the perched aquifer at the experimental site of “La Soutte” in the Vosges Mountains (France). It is located in a catchment area where several springs and streams occur along fractured volcanic and weathered plutonic rocks. The site is the object of a long-term study that uses both continuous and repeated measurements to monitor hydrogeological processes. The main results from AMT and DC resistivity techniques allow the determination of a high-resolution 3D resistivity model over a large range of depths (from 10⁰ to 10³ m). We discuss their use and propose a hydrogeological model (porosity, water conductivity and water content). We also use MRS and GPR for a detailed investigation of the shallow part of the catchment that consists of soil and weathered rocks of highly varying thickness (0 to 15 m). MRS is used to map the thickness and total water volume content by unit surface of the saturated weathered zone. It also yields estimates of the vadose zone thickness through the depth to the top of the saturated zone. Moreover, we show results from GPR CMP measurements that yield estimates of the water content and porosity in the shallowest layer (0–30 cm) by simple interpretation of the ground direct wave.     

GRIDA3—a shared resources manager for environmental data analysis and applications

GRIDA3 (Shared Resources Manager for Environmental Data Analysis and Applications) is a multidisciplinary project designed to deliver an integrated system to forge solutions to some environmental challenges such as the constant increase of polluted sites, the sustainability of natural resources usage and the forecast of extreme meteorological events. The GRIDA3 portal is mainly based on Web 2.0 technologies and EnginFrame framework. The portal, now at an advanced stage of development, provides end-users with intuitive Web-interfaces and tools that simplify job submission to the underneath computing resources. The framework manages the user authentication and authorization, then controls the action and job execution into the grid computing environment, collects the results and transforms them into an useful format on the client side. The GRIDA3 Portal framework will provide a problem-solving platform allowing, through appropriate access policies, the integration and the sharing of skills, resources and tools located at multiple sites across federated domains.     

Sequence stratigraphy of a Mesozoic carbonate platform-to-basin system in western Sicily

Sequence stratigraphic studies of the Triassic through Paleogene carbonate successions of platform, slope and basin in western Sicily (Palermo and Termini Imerese Mountains) have identified a sedimentary cyclicity mostly caused by relative oscillations of sea level. The stratigraphic successions of the Imerese and Panormide palaeogeographic domains of the southern Tethyan continental margin were studied with physical-stratigraphy and facies analysis to reconstruct the sedimentary evolution of this platform-to-basin system. The Imerese Basin is characterized by a carbonate and siliceous-calcareous succession, 1200–1400m thick, Late Triassic to Eocene in age. The strata display a typical example of a carbonate platform margin, characterized by resedimented facies with progradational stacking patterns. The Panormide Carbonate Platform is characterized by a carbonate succession, 1000–1200 m thick, Late Triassic to Late Eocene, mostly consisting of shallow-water facies with periodic subaerial exposure. The cyclic arrangement has been obtained by the study of the stratigraphic signatures (unconformities, facies sequences, erosional surfaces and stratal geometries) found in the slope successions. The recognized pattern has been compared with coeval facies of the shelf. This correlation provided evidence of sedimentary evolution, influenced by progradation and backstepping of the shelf deposits. The stratigraphic architecture of the platform-to-basin system is characterized by four major transgressive/regressive cycles during the late Triassic to late Eocene. These cycles, framed in a chronostratigraphic chart, allows the correlation of the investigated shelf-to-basin system with the geological evolution of the African continental margin during the Mesozoic, showing tectono-eustatic cycles. The first cycle, encompassing the late Triassic to early Jurassic, appears to be related to the late syn-rift stage of the continental margin evolution. The following three cycles, spanning from the Jurassic to Eocene, can be related to the post-rift evolution and to thermal subsidence changes.     

Effects of shear in the convective boundary layer: analysis of the turbulent kinetic energy budget

Effects of convective and mechanical turbulence at the entrainment zone are studied through the use of systematic Large-Eddy Simulation (LES) experiments. Five LES experiments with different shear characteristics in the quasi-steady barotropic boundary layer were conducted by increasing the value of the constant geostrophic wind by 5 m s^-1 until the geostrophic wind was equal to 20 m s^-1. The main result of this sensitivity analysis is that the convective boundary layer deepens with increasing wind speed due to the enhancement of the entrainment heat flux by the presence of shear. Regarding the evolution of the turbulence kinetic energy (TKE) budget for the studied cases, the following conclusions are drawn: (i) dissipation increases with shear, (ii) the transport and pressure terms decrease with increasing shear and can become a destruction term at the entrainment zone, and (iii) the time tendency of TKE remains small in all analyzed cases. Convective and local scaling arguments are applied to parameterize the TKE budget terms. Depending on the physical properties of each TKE budget contribution, two types of scaling parameters have been identified. For the processes influenced by mixed-layer properties, boundary layer depth and convective velocity have been used as scaling variables. On the contrary, if the physical processes are restricted to the entrainment zone, the inversion layer depth, the modulus of the horizontal velocity jump and the momentum fluxes at the inversion appear to be the natural choices for scaling these processes. A good fit of the TKE budget terms is obtained with the scaling, especially for shear contribution.     

Soil and water losses from new citrus orchards growing on sloped soils in the western Mediterranean basin

Ten representative research sites were selected in eastern Spain to assess soil erosion rates and processes in new citrus orchards on sloping soils. The experimental plots were located at representatives sites on limestone, in areas with 498 to 715 mm year^?1 mean annual rainfall, north‐facing slopes, herbicide treated, and new (less than 3 years old) plantations. Ten rainfall simulation experiments (1 h at 55 mm h^?1 on 0·25 m² plots) were carried out at each of the 10 selected study sites to determine the interill soil erosion and runoff rates. The 100 rainfall simulation tests (10 × 10 m) showed that ponding and runoff occurred in all the plots, and quickly: 121 and 195 s, respectively, following rainfall initiation. Runoff discharge was one third of the rainfall, and sediment concentration reached 10·4 g L^?1. The soil erosion rates were 2·4 Mg ha^?1 h^?1 under 5‐year return period rainfall thunderstorms. These are among the highest soil erosion rates measured in the western Mediterranean basin, similar to badland, mine spoil and road embankment land surfaces. The positive relationship between runoff discharge and sediment concentration (r² = 0·83) shows that the sediment availability is very high. Soil erosion rates on new citrus orchards growing on sloped soils are neither tolerable nor sustainable. Copyright © 2009 John Wiley & Sons, Ltd.     

Improvement of HVSR technique by self-organizing map (SOM) analysis

Data interpretation is one of the most important and thorny tasks in geosciences. Difficulties occur especially in non-invasive geophysical techniques and/or when the data that have to be analyzed are multidimensional, non-linear and highly noisy. Another important task is to ensure an efficient automatic data analysis, in order to allow a data interpretation as independent as possible from any a priori knowledge. This paper describes the post-processing application of a kind of neural network (self-organizing map, SOM) to the identification of the fundamental HVSR frequency of a given site. SOM results can be represented as two-dimensional maps, with a non-parametric mapping that projects the high dimensional original dataset in a fashion that provides both an unsupervised clustering and a highly visual representation of the data relationships. This innovative application of the SOM algorithm is presented with a case study related to the characterization of a mineral deposit.     

Wood storage in three mountain streams of the Southern Andes and its hydro‐morphological effects

This study analyses large wood (LW) storage and the associated effects on channel morphology and flow hydraulics in three third‐order mountain basins (drainage area 9–12 km²) covered in old‐growth Nothofagus forests, ranging from the temperate warm Chilean Andean Cordillera to the sub‐Antarctic Tierra del Fuego (Argentina). Amount, characteristics and dimensions of large wood (>10 cm diameter, >1 m long) were recorded, as well as their effects on stream morphology, hydraulics and sediment storage. Results show that major differences in LW abundance exist even between adjacent basins, as a result of different disturbance histories and basin dissection. Massive LW volumes (i.e. >1000 m³ ha^?1) can be reached in basins disturbed by fires followed by mass movements and debris flows. Potential energy dissipation resulting from wood dams is about a quarter of the total elevation drop in two streams, with a gross sediment volume stored behind wood dams of around 1000 m³ km^?1, which appears to be of the same order as the annual sediment yield. Finally, the presence of wood dams may increase flow resistance by up to one order of magnitude. Copyright © 2007 John Wiley & Sons, Ltd.