VLA observations of hot spots in high luminosity radio sources

VLA observations at 6 cm have been made of 16 distant luminous 3C sources that appeared to be unresolved or slightly resolved in Cambridge maps but which were known from VLBI observations to contain significant fine structure on the scale of about 1 kpc in their lobes. The general morphology of these sources is very similar to that of their nearby powerful counterparts; most of the lobes contain low brightness tails which are often directed from the hot spots towards the associated optical object. The hot spots are generally unresolved by the VLA observations; in 3C 254, 3C 268.4 and 3C 352, one of the lobes contains two hot spots.     

Reduced-order modeling for thermal recovery processes

Thermal recovery can entail considerably higher costs than conventional oil recovery, so the use of computational optimization techniques in designing and operating these processes may be beneficial. Optimization, however, requires many simulations, which results in substantial computational cost. Here, we implement a model-order reduction technique that aims at large reductions in computational requirements. The technique considered, trajectory piecewise linearization (TPWL), entails the representation of new solutions in terms of linearizations around previously simulated (and saved) training solutions. The linearized representation is projected into a low-dimensional space, with the projection matrix constructed through proper orthogonal decomposition of solution “snapshots” generated in the training step. Two idealized problems are considered here: primary production of oil driven by downhole heaters and a simplified model for steam-assisted gravity drainage, where water and steam are treated as a single “effective” phase. The strong temperature dependence of oil viscosity is included in both cases. TPWL results for these systems demonstrate that the method can provide accurate predictions relative to full-order reference solutions. Observed runtime speedups are very substantial, over 2 orders of magnitude for the cases considered. The overhead associated with TPWL model construction is equivalent to the computation time for several full-order simulations (the precise overhead depends on the number of training runs), so the method is only applicable if many simulations are to be performed.     

Partition of arsenic in soils sediments and the origin of naturally elevated concentrations in groundwater of the southern pampa region (Argentina)

Excessive arsenic concentrations above the Argentinean and WHO guidelines for drinking water (10 μg L⁻¹) affects shallow aquifers of the southern Pampean Plain (Argentina) hosted in the Pampean and the Post Pampean formations (loess and reworked loess; Plio-Pleistocene–Holocene). Health problems related to high As concentrations in drinking waters are known as Endemic Regional Chronic Hydroarsenicism. Hydrochemistry of shallow groundwaters and soil geochemistry were investigated aiming to (1) understand the partition of As in the solid phase and its relationship with unacceptable As concentrations in waters, (2) identify the provision source of As to groundwaters. Only 5% of the samples had As concentrations <10 μg L⁻¹; in 27% As concentrations ranged from 10 to 50 μg L⁻¹ and in 58% it reached 60–500 μg L⁻¹. The coarse fraction (50–2,000 μm) hosts about 27% of the total As in the solid phase, being positively correlated to Ba (p < 0.01; r ² = 0.93). About 70% is included in the <2 μm fraction and had positive correlations of As–Fe (p < 0.05; r ² = 0.85) and As–Cr (p < 0.05; r ² = 0.68). Soils and sediment sand fractions of vadose zones are the primary sources of As in shallow groundwater while adsorption–desorption processes, codisolution–coprecipitation, and evaporation during the dry seasons raise As concentrations in waters exceeding the guideline value for drinking water.     

The Catalan seismic crisis (1427 and 1428; NE Iberian Peninsula): Geological sources and earthquake triggering

The Catalan seismic crisis of the years 1427 and 1428 is one of the most destructive seismic episodes that happened in the northeastern Iberian Peninsula in historical times. The main earthquakes of this crisis occurred on March 19th 1427 in the zone around Amer (I_EMS-98 = VIII), May 15th 1427 in the vicinity of Olot (I_EMS-98 = VIII) and on February 2nd 1428 in the area close to Camprodon (I_EMS-98 = IX). There is much evidence that the Amer fault produced the first two events of this crisis, but is still uncertain which fault generated the earthquake on February 2nd 1428. Using newly available macroseismic data, the earthquake area sources of the three main earthquakes of the crisis have been obtained and they corroborate that the Amer fault may be the origin of the first two events. However, the area source corresponding to the last earthquake of the crisis cannot be associated to a single fault and indicates three possible candidates: the Vallfogona and Ribes-Camprodon thrusts and the Amer normal fault. Modeling of the Coulomb failure stress transfer has been performed to help determine the best candidate responsible for the February event. The results of the modeling points to: (a) a triggering relationship between the three main events of the crisis and (b) the Amer fault, or a similar extensional fault close and parallel to it, as the most probable origin of the earthquake on February 2nd 1428.     

Coherence between atmospheric teleconnections,Great Lakes water levels,and regional climate

We investigated the frequency domain relationships between four atmospheric teleconnections (Trans-Niño Index TNI, Pacific Decadal Oscillation PDO, Northern Annular Mode/Arctic Oscillation Index NAM/AO, and Pacific/North American PNA pattern) and water levels in the Great Lakes from 1948 to 2002 by quantifying the coherence between these time series. The levels in all Great Lakes are significantly correlated with the TNI in the frequency range (3–7)⁻¹ cycles year⁻¹, and with the PDO in interdecadal frequencies. The levels in Lakes Superior, Michigan, and Erie are significantly correlated with the PNA pattern in interdecadal frequencies, and the levels in all Great Lakes are significantly correlated with the NAM/AO in interannual frequencies.     

Comparison of mussels and semi-permeable membrane devices as intertidal monitors of polycyclic aromatic hydrocarbons at oil spill sites

Side-by-side comparisons of polycyclic aromatic hydrocarbon (PAH) concentrations in resident blue mussels (Mytilus trossulus) and in semi-permeable membrane devices (SPMDs) were made at four sites in Prince William Sound, Alaska. SPMDs were deployed for approximately 30 days on the surface of the beach sediment at three tidal elevations on each shore and in 0.5 m deep open pits in the middle intertidal zone. Total PAH (TPAH) concentrations in mussels and in SPMDs were correlated, but the PAH compositions were different. The lower molecular weight PAH were relatively more abundant in the SPMDs than in the mussels at oiled and HA sites. TPAH concentrations in SPMDs deployed in pits and mussels collected adjacent to those pits at oiled sites were higher than in SPMDs and mussels from non-pitted SPMD locations approximately 3-15 m from the pits. Pitting released buried oil making its PAH bioavailable. SPMDs deployed in the supratidal zone (+4.0 m tidal elevation) were exposed to atmospheric contaminants for a large fraction of the deployment time and accumulated primarily pyrogenic (combustion-sourced) PAH from the atmosphere. The SPMD strips supplied by the manufacturer contained significant amounts (approximately 125 ng/strip) of primarily alkylated 2-3 ring PAH. These blank levels make SPMDs unsuitable for shoreline assessments when environmental PAH concentrations are low. Consequently, where available, mussels are recommended for use in assessments of the bioavailability of buried oil residues sequestered in intertidal sediments following an oil spill. Mussels are the preferred monitoring tool when the assessments involve food-chain effects. At locations where the absence of mussels necessitates the use of SPMDs or other passive sampling devices, their limitations need to be carefully considered in the interpretation of results.     

Mercury and the estuarine marsh clam, Rangia cuneata gray. II. uptake, tissue distribution and depuration

During a two-week period, Rangia rapidly accumulates mercury (as mercuric chloride) from dilute solution (0·03–0·05 ppm) with the majority being located in gill and mantle tissue. Initial depuration (5 h) in clean seawater is rapid in all tissues. From 10–192 h concentrations of mercury in gill, foot and adductor muscles remain stable while mantle, haemolymph and viscera levels continue to fluctuate in a manner suggesting internal redistribution of mercury. After eight days of depuration, the viscera contains the most mercury and appears to be the only tissue to increase its proportionate share of the total tissue mercury. After fifteen weeks of depuration, residual mercury in whole clams is about 20% of initial concentrations. Acute decreases in salinity (15% S to 2% S) enhance Rangia's ability to depurate mercury.