Collapse and explosion in a rotating star

The collapse, bounce, shock wave and expansion of the envelope of a rotating star have been analysed in the adiabatic approximation using the particle-in-cell method. The bounce takes place first in the equatorial plane and a shock wave arises there which shortly afterwards crosses the surface of the star. In the envelope, and to a less extent in the remainder of the star, there is a fast and lasting meridional motion the direction of which changes. As a consequence of the fast meridional motion in the envelope, mass and angular momentum are transported towards the axis of rotation. If the initial star rotates fast enough this will cause a secondary radial expansion in the polar region and a mass ejection. These motions reduce the strong anisotropy caused originally by the equatorial expansion. Strong whirls may arise along the axis of rotation. In the remainder of the star the meridional motion becomes supersonic. The temperature in the envelope depends to a high degree on the choice of the equation of state. Massloss is proportional to the energy initially added. The final loss of angular momentum and of energy is quite large, both losses being about 25%.     

Geostatistical seismic inversion for non‐stationary patterns using direct sequential simulation and co‐simulation

Geostatistical seismic inversion methods are routinely used in reservoir characterisation studies because of their potential to infer the spatial distribution of the petro‐elastic properties of interest (e.g., density, elastic, and acoustic impedance) along with the associated spatial uncertainty. Within the geostatistical seismic inversion framework, the retrieved inverse elastic models are conditioned by a global probability distribution function and a global spatial continuity model as estimated from the available well‐log data for the entire inversion grid. However, the spatial distribution of the real subsurface elastic properties is complex, heterogeneous, and, in many cases, non‐stationary since they directly depend on the subsurface geology, i.e., the spatial distribution of the facies of interest. In these complex geological settings, the application of a single distribution function and a spatial continuity model is not enough to properly model the natural variability of the elastic properties of interest. In this study, we propose a three‐dimensional geostatistical inversion technique that is able to incorporate the reservoir's heterogeneities. This method uses a traditional geostatistical seismic inversion conditioned by local multi‐distribution functions and spatial continuity models under non‐stationary conditions. The procedure of the proposed methodology is based on a zonation criterion along the vertical direction of the reservoir grid. Each zone can be defined by conventional seismic interpretation, with the identification of the main seismic units and significant variations of seismic amplitudes. The proposed method was applied to a highly non‐stationary synthetic seismic dataset with different levels of noise. The results of this work clearly show the advantages of the proposed method against conventional geostatistical seismic inversion procedures. It is important to highlight the impact of this technique in terms of higher convergence between real and inverted reflection seismic data and the more realistic approximation towards the real subsurface geology comparing with traditional techniques.     

Assessment of toxicological status of a SW Mediterranean segment population of striped dolphin (Stenella coeruleoalba) using skin biopsy

Various studies have revealed high concentrations of contaminants such as organochlorines (OCs) and heavy metals in Mediterranean cetaceans. A geographical trend of contamination (PCBs and DDTs) has been found for striped dolphin (Stenella coeruleoalba). In this study we used a non-lethal approach (skin biopsy) to investigate bioaccumulation of OCs, including polychlorobiphenyls (PCBs), DDTs, polychlorodibenzo-p-dioxins (PCDDs), polychlorodibenzofurans (PCDFs), trace elements (Hg, Cd, Pb) and CYP1A activity (BPMO) in nine striped dolphins sampled in the Aeolian area (Sicily - Italy) in summer 2002. The arithmetic mean value of BPMO activity in this group was 43.46 AUF/g tissue/h. This value is approximately 3 times and 5 times lower, respectively, than the value found in the Ionian and in the Ligurian groups. Skin biopsies of striped dolphins emerged as a suitable material for assessing the toxicological status of the various Mediterranean groups.     

Spring distribution of dissolved organic matter in a system encompassing the Northeast Water Polynya: Implications for early-season sources and sinks

This study addresses sources and diagenetic state of early-season dissolved organic matter (DOM) in the Northeast Water Polynya (NEWP) area northeast of Greenland from distributions of humic substance fluorescence (HSfl), dissolved organic carbon (DOC), and dissolved organic nitrogen (DON) in the water column inside and outside the NEWP area. The water masses of the polynya area had acquired their spring/summer temperature–salinity characteristics at the time of sampling, and also had individual, different DOM signatures. DOC concentrations were variable within and among water masses in the polynya area, indicating patchy local sources and sinks of DOC. PySW and polynya intermediate water (PyIW) had higher average DON concentrations and average lower C:N ratios than polynya bottom water (PyBW), indicating a larger fraction of fresh DOM in PySW and PyIW than in PyBW. Ice-covered, polynya area surface waters (PySW) had higher DOC concentrations (113±14 μM, n=68) than surface water (SW) outside the polynya area (96±18 μM, n=6). The DOM C:N ratios in a low-salinity, ice-melt subgroup of PySW samples indicate labile material, and these low-salinity surface waters appeared to have a local DOC and DON source. In contrast, HSfl was significantly lower inside than outside the NEWP area. Despite the lower HSfl values within the NEWP area, the PySW values were high when compared to open-ocean water. There were no local terrestrial sources for HSfl to the NEWP area and the East Greenland Current is therefore proposed as a likely source of allochtonous HSfl. When HSfl was used as a conservative tracer, up to 70% of the water in PySW and PyIW was found to be derived from SW, which contains a high fraction of water from the East Greenland Current. Similarly, a mixing model based on HSfl indicated that 80% of early-season DOC and 90–100% of early-season DON in PySW and PyIW were derived from SW, indicating a potentially high fraction of terrestrially-derived, relatively refractory DOM in the early-season NEWP area.     

Characterization of dissolved organic matter in anoxic rock extracts and in situ pore water of the Opalinus Clay

Dissolved organic matter (DOM) from the Opalinus Clay, a potential host rock for the disposal of radioactive waste, was isolated under strictly anoxic conditions from ground rock material and compared with DOM of in situ pore water samples. For the extractions, deionized water, synthetic pore water (SPW, water containing all major ions at pore water concentrations but no organic matter) and 0.1 M NaOH were used. The influence of the solid-to-liquid ratio, extraction time, acid-pretreatment and O₂ exposure of the rock material on the isolated DOM were investigated. Liquid chromatography coupled with a total organic C detector (LC-OCD) and reverse-phase ion chromatography were used to characterize the DOM size distributions and to determine the low molecular weight organic acid (LMWOA) contents in the pore water samples and the rock extracts.The results revealed that only a small portion of the total organic C of the rock material (<0.38%) was extractable, even after removal of carbonates by acid-pretreatment. The concentrations of dissolved organic C (DOC) were found to range from 3.9 ± 0.4 to 8.0 ± 0.8 mg/L in the anoxic extracts. The pore waters exhibited similar DOC concentrations ranging from 1.2 to 15.8 ± 0.5 mg/L. The analysis by LC-OCD showed that the DOM extracted under anoxic conditions and the pore water DOM mainly consisted of hydrophilic compounds of less than 500 Da. The DOM extracted with SPW was most similar in size to the pore water DOM. Grinding the rock under oxic conditions increased the DOC yields and shifted the size distribution toward higher molecular weight compounds compared to the strictly anoxic treatment. Acetate, lactate and formate were identified in all extracts and in the pore water. In total, LMWOA accounted for 36% of the total DOC in both pore water and SPW extracts. The results imply that controlled anoxic conditions and the use of SPW as an extractant are required to isolate DOM from Opalinus Clay rocks which most resembles the in situ pore water DOM with respect to its size distribution and the LMWOA contents.     

A locally conservative variational multiscale method for the simulation of porous media flow with multiscale source terms

We present a variational multiscale mixed finite element method for the solution of Darcy flow in porous media, in which both the permeability field and the source term display a multiscale character. The formulation is based on a multiscale split of the solution into coarse and subgrid scales. This decomposition is invoked in a variational setting that leads to a rigorous definition of a (global) coarse problem and a set of (local) subgrid problems. One of the key issues for the success of the method is the proper definition of the boundary conditions for the localization of the subgrid problems. We identify a weak compatibility condition that allows for subgrid communication across element interfaces, a feature that turns out to be essential for obtaining high-quality solutions. We also remove the singularities due to concentrated sources from the coarse-scale problem by introducing additional multiscale basis functions, based on a decomposition of fine-scale source terms into coarse and deviatoric components. The method is locally conservative and employs a low-order approximation of pressure and velocity at both scales. We illustrate the performance of the method on several synthetic cases and conclude that the method is able to capture the global and local flow patterns accurately.