Compton-thick X-ray absorption in the Seyfert galaxies Tololo 0109383 and ESO 138G1

We present analyses of the ASCA X-ray spectra of two Seyfert galaxies, Tololo 0109383 and ESO 138G1. In both cases, spectral fitting reveals two statistically acceptable continuum models: Compton reflection and partial covering. Both spectra have strong iron K lines, with equivalent widths greater than 1.5 keV. These large equivalent widths are suggestive of heavier obscuration than that directly indicated by the partial-covering models (  210²³ cm^-2),  with the actual column densities being 'Compton-thick' (i.e.   N _H1.510²⁴ cm^-2).  We use the hard X-ray/[O  iii ] flux correlation for Seyferts and data from the literature to provide additional support for this hypothesis. Since Tololo 0109383 is known to have optical type 1 characteristics such as broad Balmer line components and Fe  ii emission, this result marks it as a notable object.     

Rapid invasion of Crassostrea gigas into the German Wadden Sea dominated by larval supply

Invasions of non-indigenous species into coastal habitats have been a frequent phenomenon in the last decades, sometimes with significant impact on the receiving ecosystem. However, the understanding of the entire process and especially the relative importance of larval supply and local recruitment remains unclear. In this study, we simulate the invasion of a benthic invertebrate into a previously uncolonised habitat over several years and validate the results with field data. Therefore, we present field data from a monitoring programme revealing the rapid invasion of the oyster Crassostrea gigas into the East Frisian Wadden Sea, North Sea, between 2003 and 2005. The applied model combines a simple, spatially-explicit population dynamics model for the adult stage with a particle tracking model for the larval stage of the life cycle. Simulation results are able to reproduce the large-scale pattern of the field data and indicate a domination of larval supply on the population dynamics in the early stage of the invasion. Though monitoring and simulations suggest a single larval source outside the study area in the west, the population dynamics in the eastern part is only explainable with an additional source within the study area attributed to an unintentional input of juveniles by mussel fishery. High sensitivities to uncertain parameters result in distinct deviations between monitoring and simulations at particular sites. Especially the impact of site-specific variations of the post-settlement mortality underlines the variability of local recruitment conditions and indicates the need for spatially resolved information for exact predictions.     

Changes in timber haul emissions in the context of shifting forest management and infrastructure

Background  

Although significant amounts of carbon may be stored in harvested wood products, the extraction of that carbon from the forest generally entails combustion of fossil fuels. The transport of timber from the forest to primary milling facilities may in particular create emissions that reduce the net sequestration value of product carbon storage. However, attempts to quantify the effects of transport on the net effects of forest management typically use relatively sparse survey data to determine transportation emission factors. We developed an approach for systematically determining transport emissions using: 1) -remotely sensed maps to estimate the spatial distribution of harvests, and 2) - industry data to determine landscape-level harvest volumes as well as the location and processing totals of individual mills. These data support spatial network analysis that can produce estimates of fossil carbon released in timber transport.     

Wide field monitoring of the X-ray sky using Rotation Modulation Collimators

Wide field monitoring is of particular interest in X-ray astronomy due to the strong time-variability of most X-ray sources. Not only does the time-profiles of the persistent sources contain characteristic signatures of the underlying physical systems, but, additionally, some of the most intriguing sources have long periods of quiesense in which they are almost undetectable as X-ray sources, interspersed with relatively brief periods of intense outbursts, where we have unique opportunities of studying dynamical effects, in, for instance, the evolution of accretion discs. Another question for which wide field monitors may provide key information, is the origin and nature of the cosmic gamma ray bursts.Rotation Modulation Collimators (RMC's) were originally introduced in X-ray astronomy to provide accurate source localizations over extended fields. This role has since been taken over by the grazing incidence telescope systems. The potential of the RMC's as wide field monitors have recently been demonstrated by the WATCH instruments on GRANAT and EURECA. It now appears likely, that for use on large, 3-axis stabilized spacecraft, a pinhole camera system may provide better sensitivity than an RMC-system of corresponding physical dimensions. But due to its simplicity, low data rate, and ability to work on spin stabilized (micro)satellites, the RMC wide field monitor may still have a role to play in the X-ray astronomy of the future.     

Simulation of the size distribution and erosivity of raindrops and throughfall drops

This paper presents a model that simulates the size distribution and erosivity of raindrops and throughfall drops. It utilizes existing models of rainfall drop size distribution and fall velocity and combines them with newly collated evidence of throughfall drop size distributions. A sensitivity analysis reveals that the model is sensitive to parameters that are easily measured or estimated: rainfall intensity, the mean volume drop diameter of the intercepted throughfall, canopy cover, and canopy height. The results of the model may be used at two levels. Firstly, to calculate specifically the size and fall velocity of individual drops, parameters that are needed in studies examining the response of soil surfaces to forces applied by rainfall. Secondly, to produce erosivity indices, based on rainfall intensity but which take account of the effects of a vegetation canopy. The paper shows that while the kinetic energy of rainfall (E(0), J mm^?1 m^?2) may be calculated from an equation of the familiar form: the kinetic energy of throughfall under any canopy may be calculated by combining this equation with another that relates the energy of drops under a 100 per cent canopy cover (E(100)) and the canopy height: .     

An experimental study of two-dimensional atmospheric gas dispersion near two objects

Two-dimensional gas dispersion in the atmosphere was investigated experimentally using an atmospheric boundary-layer wind tunnel. Argon gas, which is one and one half times heavier than air, was injected two-dimensionally and uniformly near two square objects at the rates of 3.55 and 4.93 m³/min per lateral meter from the bottom of the wind tunnel floor through a porous metal plate. The gas injection source was located at one object distance upstream of the first square object. Gas concentrations and velocities of the flow field were measured using an aspirating hot-film probe and a low velocity flow analyzer, respectively. The gas was dispersed no higher than approximately 2.0 object heights near the objects, and dispersed no higher than 3.5 object heights at the location of downwind distances of nine object lengths for the injection rates tested. The gas concentrations between the injection source and the first object were about 4 to 5 times higher than the gas concentrations of the other locations. The gas concentrations were 2 to 3% in the recirculation zone between the two objects, and were less than 2% behind the second object. The air-gas mixtures in the recirculation zone between the two objects and within the wake recirculation bubble behind the second object were well mixed and no gravitational settlement was detected in those regions. However, as the mixture moved down-stream, the gravitational settlement occurred beyond the wake recirculation bubble. This paper demonstrates that it is possible to model a two-dimensional heavy gas release in the atmosphere using wind-tunnel simulation with properly matched similitude parameters.     

Spatial and Temporal Variability in Estuary Habitat Use by American Alligators

Estuarine habitat occupied by Alligator mississippiensis, a primarily freshwater species, is spatially and temporally heterogeneous largely due to a salinity gradient that fluctuates. Using long-term night light survey data, we examined seasonal patterns in alligators’ habitat use by size classes in midstream and downstream estuary zones of Shark River, Everglades National Park, in southern Florida. We observed predominantly large-sized alligators (total length?≥?1.75 m); observations of alligators in the small size classes (0.5 m?≤?total length?<?1.25 m) were rare especially in the higher-salinity downstream zone. The density of alligators in the downstream zone was lower than that of the midstream zone during the dry season when salinity increases due to reduced precipitation. Conversely, the density of the large size alligators was higher in the downstream zone than in the midstream zone during the wet season, likely because of reduced salinity. We also found a significant declining trend over time in the number of alligators in the dry season, which coincides with the reported decline in alligator relative density in southern Florida freshwater wetlands. Our results indicated high adaptability of alligators to the fluctuating habitat conditions. Use of estuaries by alligators is likely driven in part by physiology and possibly by reproductive cycle, and our results supported their opportunistic use of estuary habitat and ontogenetic niche shifts.     

Water availability and land subsidence in the Central Valley,California, USA

The Central Valley in California (USA) covers about 52,000 km² and is one of the most productive agricultural regions in the world. This agriculture relies heavily on surface-water diversions and groundwater pumpage to meet irrigation water demand. Because the valley is semi-arid and surface-water availability varies substantially, agriculture relies heavily on local groundwater. In the southern two thirds of the valley, the San Joaquin Valley, historic and recent groundwater pumpage has caused significant and extensive drawdowns, aquifer-system compaction and subsidence. During recent drought periods (2007–2009 and 2012-present), groundwater pumping has increased owing to a combination of decreased surface-water availability and land-use changes. Declining groundwater levels, approaching or surpassing historical low levels, have caused accelerated and renewed compaction and subsidence that likely is mostly permanent. The subsidence has caused operational, maintenance, and construction-design problems for water-delivery and flood-control canals in the San Joaquin Valley. Planning for the effects of continued subsidence in the area is important for water agencies. As land use, managed aquifer recharge, and surface-water availability continue to vary, long-term groundwater-level and subsidence monitoring and modelling are critical to understanding the dynamics of historical and continued groundwater use resulting in additional water-level and groundwater storage declines, and associated subsidence. Modeling tools such as the Central Valley Hydrologic Model, can be used in the evaluation of management strategies to mitigate adverse impacts due to subsidence while also optimizing water availability. This knowledge will be critical for successful implementation of recent legislation aimed toward sustainable groundwater use.     

A Probabilistic Expert System Approach for Sea Mine Burial Prediction

Knowledge of the extent of burial of bottom sitting sea mines is critical to mine detection due to the significantly degraded capabilities of mine-hunting systems when the mines are buried. To provide an enhanced capability for predicting mine burial in support of U.S. Navy mine countermeasure (MCM) operations, an expert system approach to predicting sea mine burial has been developed. This expert system serves as a means to synthesize previous and current research on sea mine burial due to impact upon deployment and subsequently due to scour, the two dominant burial mechanisms in littoral waters. Prediction systems for impact and scour burial have been implemented as simple Bayesian networks whose probabilistic basis provides means of accounting for the inherent uncertainties associated with mine deployment methods, simplified physics-based burial models, and environmental variability. Examples of burial predictions and comparisons to results from field experiments are illustrated. In addition, a proposed risk metric is developed and applied to provide a geospatial mapping of mine burial probability.