Automated probabilistic classification of transients and variables

There is an increasing number of large, digital, synoptic sky surveys, in which repeated observations are obtained over large areas of the sky in multiple epochs. Likewise, there is a growth in the number of (often automated or robotic) follow‐up facilities with varied capabilities in terms of instruments, depth, cadence, wavelengths, etc., most of which are geared toward some specific astrophysical phenomenon. As the number of detected transient events grows, an automated, probabilistic classification of the detected variables and transients becomes increasingly important, so that an optimal use can be made of follow‐up facilities, without unnecessary duplication of effort. We describe a methodology now under development for a prototype event classification system; it involves Bayesian and Machine Learning classifiers, automated incorporation of feedback from follow‐up observations, and discriminated or directed follow‐up requests. This type of methodology may be essential for the massive synoptic sky surveys in the future. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Statistical inference in the presence of an inclination effect in laboratory radiative shock experiments

A laser-driven experiment produces images of dense shocked material by x-ray transmission. The post-shock material is sufficiently dense that no significant signal passes through the dense layer, and therefore the shock compression cannot be directly measured by comparing transmitted intensities. One could try to determine the shock compression ratio by observing the ratio of the total distance travelled by the shock to the dense post-shock layer width, but small deviations of the angle of the shock with respect to the angle of imaging create large asymmetric errors in observation. A statistical approach to recovering shock compression by appropriately combining data from several experiments is developed, using fits to a simple model for the shock and shock tube geometry.     

Long‐term effects of revegetation on soil hydrological processes in vegetation‐stabilized desert ecosystems

Planting of sand‐binding vegetation in the Shapotou region on the southeastern edge of the Tengger Desert began in 1956. The revegetation programme successfully stabilized formerly mobile dunes in northern China, permitting the operation of the Baotou‐Lanzhou railway. Long‐term monitoring has shown that the revegetation programme produced various ecological changes, including the formation of biological soil crusts (BSCs). To gain insight into the role of BSCs in both past ecological change and current ecological evolution at the revegetation sites, we used field measurements and HYDRUS‐1D model simulations to investigate the effects of BSCs on soil hydrological processes at revegetated sites planted in 1956 and 1964 and at an unplanted mobile dune site. The results demonstrate that the formation of BSCs has altered patterns of soil water storage, increasing the moisture content near the surface (0–5 cm) while decreasing the moisture content in deeper layers (5–120 cm). Soil evaporation at BSC sites is elevated relative to unplanted sites during periods when canopy coverage is low. Rainfall infiltration was not affected by BSCs during the very dry period that was studied (30 April to 30 September 2005); during periods with higher rainfall intensity, differences in infiltration may be expected due to runoff at BSC sites. The simulated changes in soil moisture storage and hydrological processes are consistent with ongoing plant community succession at the revegetated sites, from deep‐rooted shrubs to more shallow‐rooted herbaceous species. Copyright © 2009 John Wiley & Sons, Ltd.     

The vertical distribution of macro-insects migrating in the nocturnal boundary layer: A radar study

A special-purpose radar has been used to observe the vertical distribution of large, strong-flying insects migrating in the nocturnal boundary layer over the central-western plains region of New South Wales. During the period of take-off flight at dusk, the density of insects decreased monotonically with height, and a distribution of this type persisted for much of the night in the zone of steady temperature lapse extending from the top of the inversion layer to the flight ceiling at about 1 km. Later in the night, the insects often became concentrated in the warm air at the top of the inversion layer. The lower boundary of this concentration sometimes became sharply defined, but above the zone of maximum insect density there was usually a smooth decrease of insect numbers with altitude. When the boundary layer was disturbed by an atmospheric density current, the direction and vertical distribution of the migration was permanently changed; solitary wave disturbances, however, had only a transient effect.     

Geochemistry of tin, tungsten and molybdenum in Swedish proterozoic granitoids: Their potential use in regional mineral exploration

The primary aim of this broad regional study is to statistically determine the Li-Sn-W-Mo-bearing potential of various granitoids using geochemical criteria. Computer based, univariate and multivariate statistical methods are applied to major- and trace-element data from about 660 granitic rock samples and over 800 major element analyses, selected from the Swedish geological literature. The granitoids are subdivided following earlier geotectonic chronologic and newer geochemical-statistical principles.Most granite types occurring in known Sn-W mineralized areas, except the granites around the W deposit of Baggetorp, were identified as potentially W-Sn-bearing. That is, they show significantly high mean and variance values for W and/or Sn as well as promising values of the probability parameters for these elements, compared to corresponding statistics for a calculated Swedish average granitoid (SAG).Evidence of very high total variability of Li, Sn and W within the individual granite types suggests the need for further tests, to control the variability errors due to sampling and preparation and errors of chemical analysis. These sources of error may obscure natural elemental heterogeneity of the granite type that is of interest in geochemical prospecting.Interpretations of Sn, W and Li frequency distribution patterns, petrochemical trends and multivariate similarity tests suggest that the primary chemistry of the granitoids is overprinted by (a) postmagmatic processes of broad regional nature, which have similarly affected the individual granite types, and (b) a wide variety of secondary alterations of local character. These conclusions imply that potential Sn and W deposits may be sought within all Swedish Proterozoic granitoids and their within all Swedish Proterozoic granitoids and their immediate sorroundings, where susch processes have redistributed and concentrated these where such processes have redistributed and concentrated these elements. However, the granites which are highly differentiated, Sn-W-Li-U-Th-F-enriched, and strongly and strongly magnetic are particularly promising target areas for further, extensive rock-geochemical prospecting and other exploration surveys. rock-geochemical prospecting and other exploration surveys.     

The oxidation state of europium as an indicator of oxygen fugacity

The distribution of Eu between plagioclase feldspar and magmatic liquid has been determined experimentally for basaltic and andesitic systems as a function of temperature and oxygen fugacity at one atmosphere total pressure. Using the approach of Philpotts the ratios $\text{Eu}{}^{\mathrm{2+}}\text{Eu}{}^{\mathrm{3+}}$ in plagioclase and coexisting magmatic liquid have been calculated. These ratios appear to be simply related to oxygen fugacity for the bulk compositions studied here. Using published trace element distribution data for natural rocks oxygen fugacities may be calculated from these experimental results. For terrestrial basalts calculated oxygen fugacities average 10^?7 with little dispersion from this value. Andesites average 10^?8.1 with considerable dispersion, while dacites and rhyodacites average 10^?9.1, also with considerable dispersion. Oxygen fugacities for lunar ferrobasalts cluster tightly around 10^?12.7. Data on achondritic meteorites are limited, but calculations indicate oxygen fugacities of two-to-five orders of magnitude lower than lunar ferrobasalts.     

The Cartesian method for solving partial differential equations in spherical geometry

Cartesian coordinates are used to solve the nonlinear shallow-water equations on the sphere. The two-dimensional equations, in spherical coordinates, are first embedded in a three-dimensional system in a manner that preserves solutions of the two-dimensional system. That is, solutions of the three-dimensional system, with appropriate initial conditions, also solve the two-dimensional system on the surface of the sphere. The higher dimensional system is then transformed to Cartesian coordinates. Computations are limited to the surface of the sphere by projecting the equations, gradients, and solution onto the surface. The projected gradients are approximated by a weighted sum of function values on a neighboring stencil. The weights are determined by collocation using the spherical harmonics in trivariate polynomial form. That is, the weights are computed from the requirement that the projected gradients are near exact for a small set of spherical harmonics. The method is applicable to any distribution of points and two test cases are implemented on an icosahedral geodesic grid. The method is both vectorizable and parallelizable.     

Plagioclase—melt equilibria

The crystallization of plagioclase feldspar from magmatic liquid has been investigated experimentally under equilibrium conditions at 1 atm total pressure in the temperature range 1400-1095°C. Natural and synthetic melts of composition basalt to rhyolite were used, crystallizing plagioclase of composition An₈₉-An₃₂.The experimental results are analyzed initially in terms of elemental plagioclase/melt partition coefficients (D). D_Si is always less than unity and is invariant with temperature. D_A1 is always greater than unity and is relatively insensitive to temperature. D_Na is less than unity above 1200°C and is strongly dependent upon temperature. D_Ca is greater than unity below 1430°C and is strongly dependent upon temperature.Analysis of the temperature-dependence of equilibrium constants for plagioclase-melt formation and exchange reactions in which several mixing models for the melt are considered, leads to the conclusion that, with appropriate choice of melt-components, the melt-components mix quasi-ideally. At fixed temperature in the absence of H₂O, the equilibrium constant for the equilibrium of albite with the melt is insensitive to changes in melt-composition, and is insensitive to changes in pressure up to at least 10 kbars. As a consequence the composition of plagioclase crystallizing at known temperature and at low total pressure from a dry melt of known composition may be predicted []. However, the equilibrium constant is sensitive to changes in water pressure.The analysis further suggests that Na is intimately associated with tetrahedrally-coordinated Al in the melt, while Ca appears to be partitioned between at least two distinct melt-sites.     

XMM-Newton observations of the isolated neutron star 1RXS J214303.7+065419/RBS1774

We report XMM-Newton observations of the isolated neutron star RBS1774 and confirm its membership as an XDINS. The X-ray spectrum is best fit with an absorbed blackbody with temperature kT=101 eV and absorption edge at 0.7 keV. No power law component is required. An absorption feature in the RGS data at 0.4 keV is not evident in the EPIC data, but it is not possible to resolve this inconsistency. The star is not seen in the UV OM data to m _AB ∼21. There is a sinusoidal variation in the X-ray flux at a period of 9.437 s with an amplitude of 4%. The age as determined from cooling and magnetic field decay arguments is 10⁵–10⁶ yr for a neutron star mass of 1.35–1.5 M_⊙.      

Time‐transgressive tunnel‐valley infill revealed by a three‐dimensional sedimentary model,Hamburg, north‐west Germany

Deep, elongated incisions, often referred to as tunnel valleys, are among the most characteristic landforms of formerly glaciated terrains. It is commonly thought that tunnel valleys were formed by meltwater flowing underneath large ice sheets. The sedimentary infill of these features is often highly intricate and therefore difficult to predict. This study intends to improve the comprehension of the sedimentology and to establish a conceptual model of tunnel‐valley infill, which can be used as a predictive tool. To this end, the densely sampled, Pleistocene tunnel valleys in Hamburg (north‐west Germany) were investigated using a dataset of 1057 deep wells containing lithological and geophysical data. The stratigraphic correlations and the resulting three‐dimensional lithological model were used to assess the spatial lithological distributions and sedimentary architecture. The sedimentary succession filling the Hamburg area tunnel valleys can be subdivided into three distinct units, which are distinguished by their inferred depositional proximity to the ice margin. The overall trend of the succession shows a progressive decrease in transport energy and glacial influence through time. The rate of glacial recession appears to have been an important control on the sedimentary architecture of the tunnel‐valley fill. During periods of stagnation, thick ice‐proximal deposits accumulated at the ice margin, while during rapid recession, only a thin veneer of such coarse‐grained sediments was deposited. Ice‐distal and non‐glaciogenic deposits (i.e. lacustrine, marine and terrestrial) fill the remaining part of the incision. The infill architecture suggests formation and subsequent infill of the tunnel valleys at the outer margin of the Elsterian ice sheet during its punctuated northwards recession. The proposed model shows how the history of ice‐sheet recession determines the position of coarse‐grained depocentres, while the post‐glacial history controls the deposition of fines through a progressive infill of remnant depressions.