Collimation of a Central Wind by a Disk-Associated Magnetic Field

We present the results of time-dependent, numerical magnetohydrodynamic simulations of a realistic young stellar object outflow model with the addition of a disk-associated magnetic field. The outflow produced by the magnetic star-disk interaction consists of an episodic jet plus a wide-angle wind with an outflow speed comparable to that of the jet (100–200 km s^-1). An initially vertical field of ? 0.1 Gauss, embedded in the disk, has little effect on the wind launching mechanism, but we show that it collimates the entire flow (jet + wide wind) at large (several AU) distances. The collimation does not depend on the polarity of the vertical field. We also discuss the possible origin of the disk-associated field.     

Dissolved Inorganic Nitrogen,Soluble Reactive Phosphorous,and Microbial Pollutant Loading from Tropical Rural Watersheds in Hawai'i to the Coastal Ocean During Non-Storm Conditions

This study quantifies dissolved inorganic nitrogen (DIN), soluble reactive phosphorous (SRP), and microbial pollutant inputs to a tropical embayment, Hanalei Bay, Kaua'i, Hawai'i from rural watersheds during two field excursions during non-storm conditions. We employ land cover analysis and a suite of nucleic acid fecal source tracking markers (host-specific Bacteroidales and human enterovirus) to identify sources of pollutants to the bay. The highest concentrations of DIN and SRP are in streams draining watersheds with large areas of cultivated land, suggesting fertilizer is a source of these nutrients to the streams and coastal waters. Pollutant areal loading correlates with the fractions of urban and cultivated land cover. Microbial source tracking indicates the presence of human, pig, and ruminant feces in the streams. This work provides preliminary evidence that human development affects loading of DIN, SRP, and microbial pollutants to tropical coastal waters; further study is needed to confirm this. Additionally, results point to a mix of microbial pollutant sources.     

Fe xxv and Fe xxvi lines from low-velocity, photoionized gas in the X-ray spectra of active galactic nuclei

We have calculated the equivalent widths of the absorption lines produced by Fe  xxv and Fe  xxvi in a Compton-thin, low-velocity photoionized material illuminated by the nuclear continuum in active galactic nuclei. The results, plotted against the ionization parameter and the column density of the gas, are a complement to those presented by Bianchi & Matt for the emission lines from the same ionic species. As an extension to the work by Bianchi & Matt, we also present a qualitative discussion on the different contributions to the He-like iron emission line complex in the regimes where recombination or resonant scattering dominates, providing a useful diagnostic tool to measure the column density of the gas. Future high-resolution missions (e.g. Astro-E2 ) will allow us to fully take advantage of these plasma diagnostics. In the meantime, we compare our results with an up-to-date list of Compton-thick and unobscured (at least at the iron line energy) Seyfert galaxies with emission and/or absorption lines from H- and He-like iron observed with Chandra and XMM–Newton .     

Limitations of Current Approaches for Predicting Groundwater Vulnerability from PFAS Contamination in the Vadose Zone

Published literature for reported sorption coefficients (K_d) of eight anionic per- and polyfluoroalkyl substances (PFAS) in soil was reviewed. K_d values spanned three to five log units indicating that no single value would be appropriate for use in estimating PFAS impacts to groundwater using existing soil-water partition equations. Regression analysis was used to determine if the soil or solution parameters might be used to predict K_d values. None of the 15 experimental parameters collected could individually explain variability in reported K_d values. Significant associations between K_d and soil calcium and sodium content were found for many of the selected PFAS, suggesting that soil cation content may be critical to PFAS sorption, as previously noted in sources like Higgins and Luthy (2006), while organic carbon content was significant only at elevated levels (>5%). Unexplained discrepancies between the results from studies where PFAS were introduced to soil and desorbed in the laboratory and those that used material from PFAS-impacted sites suggest that laboratory experiments may be overlooking some aspects critical to PFAS sorption. Future studies would benefit from the development and use of standardized analytical methods to improve data quality and the establishment of soil parameters appropriate for collection to produce more complete data sets for predictive analysis.     

Dike emplacement near Parícutin volcano,Mexico in 2006

A major seismic swarm occurred near Parícutin volcano between the end of May and early July 2006. More than 700 earthquakes with magnitude (M _L ) exceeding 2.4 were located. Parícutin, located in the Michoacán–Guanajuato volcanic field in western Mexico, is well known as the site of the 1943 eruption in which a new 400 m cinder cone was constructed in what had been farmland. The 2006 swarm exhibits all of the characteristics typically associated with swarms of volcanic origins. The earthquake rate showed the typical ramp up and ramp down over the course of several days. Magnitudes were evenly distributed in time with a notably high b-value of 2.45. The earthquake locations cluster around a northeast-striking trend extending approximately 6 km. Over the first two weeks, hypocenters migrated steadily a few hundred meters per day, rising from 9 to 5 km depth and moving northeast about 5 km. On approximately June 7, the ascent of hypocenters stalled. For the next three weeks, hypocenters held their depth while migrating laterally back to the southwest. Focal mechanisms during the first part of the swarm reflected the increased stress caused by dike inflation. Following June 7, the stress orientation changed and became more consistent with the inflation of horizontal sill-like structures. Though only limited information is available from the seismic swarm preceding the 1943 eruption, several features, including the swarm duration and magnitude relationships, were comparable to those of the 2006 episode. The strong indicators of a magmatic origin to the 2006 swarm suggest that at this location there are few, if any, traditional seismic discriminants that could be used to distinguish which seismic swarms and dike emplacement events might culminate in eruption.