The charge distribution on interstellar grains—The effect of induced charge

A calculation of the equilibrium charge acquired by interstellar grains is given, which takes account of polarization charges that are induced in a grain by incident ions and electrons.Both metal and dielectric grains are considered and photoionization of the latter grains by UV radiation is taken into account where necessary. It is found that the inclusion of the polarization charges in the calculation is only important in gas clouds where the mean charge on a grain is low (<1e); that is, for HI regions and dense molecular clouds. In such clouds, the effect of the polarization charges is to increase the amount of negative charge acquired by a grain. A discussion is given concerning the validity of the classical electrostatic theory employed in the paper for small grains of radius 10^–6 cm, and some astrophysical consequences of the modification of the grain charge by polarization effects are considered.     

Automated Target Detection and Discrimination Using Constrained Kurtosis Maximization

Exploiting hyperspectral imagery without prior information is a challenge. Under this circumstance, unsupervised target detection becomes an anomaly detection problem. We propose an effective algorithm for target detection and discrimination based on the normalized fourth central moment named kurtosis, which can measure the flatness of a distribution. Small targets in hyperspectral imagery contribute to the tail of a distribution, thus making it heavier. The Gaussian distribution is completely determined by the first two order statistics and has zero kurtosis. Consequently, kurtosis measures the deviation of a distribution from the background and is suitable for anomaly/target detection. When imposing appropriate inequality constraints on the kurtosis to be maximized, the resulting constrained kurtosis maximization (CKM) algorithm will be able to quickly detect small targets with several projections. Compared to the widely used unconstrained kurtosis maximization algorithm, i.e., fast independent component analysis, the CKM algorithm may detect small targets with fewer projections and yield a slightly higher detection rate.     

Studying the Deep Structure of Elbrus Volcano by Microseismic Sounding

This paper presents results from a study of the deep structure of the Elbrus edifice and adjacent areas using geophysical techniques. We confirmed the existence of a shallow magma chamber, derived a more accurate location of the chamber in the host rocks and its characteristic dimensions, and compared new results with known studies. More accurate estimates have been obtained for the temperature at the top of the magma chamber and new evidence is adduced concerning the deep structure of the fluid magmatic systems in the Elbrus volcanic area.     

The impact of rural land management changes on soil hydraulic properties and runoff processes: results from experimental plots in upland UK

To develop an evidence base to help predict the impacts of land management change on flood generation, four experimental sites were established on improved grassland used for sheep grazing at the Pontbren catchment in upland Wales, UK. At each site, three plots were established where surface runoff was measured, supplemented by measurements of soil infiltration rates and soil and vegetation physical properties. Following baseline monitoring, treatments were applied to two of the plots: exclusion of sheep (ungrazed) and exclusion of sheep and planting with native broadleaf tree species (tree planted), with the third plot acting as a control (grazed pasture). Due to a particularly dry summer that occurred pre‐treatment, the soil hydrological responses were initially impacted by the effects of the climate on soil structure. Nevertheless, treatments did have a clear influence on soil hydrological response. On average, post‐treatment runoff volumes were reduced by 48% and 78% in ungrazed and tree‐planted plots relative to the control, although all results varied greatly over the sites. Five years following treatment application, near‐surface soil bulk density was reduced and median soil infiltration rates were 67 times greater in plots planted with trees compared to grazed pasture. The results illustrate the potential use of upland land management for ameliorating local‐scale flood generation but emphasise the need for long‐term monitoring to more clearly separate the effects of land management from those of climatic variability. Copyright © 2013 John Wiley & Sons, Ltd.     

Non-linear fluid dynamics of eccentric discs

A new theory of eccentric accretion discs is presented. Starting from the basic fluid-dynamical equations in three dimensions, I derive the fundamental set of one-dimensional equations that describe how the mass, angular momentum and eccentricity vector of a thin disc evolve as a result of internal stresses and external forcing. The analysis is asymptotically exact in the limit of a thin disc, and allows for slowly varying eccentricities of arbitrary magnitude. The theory is worked out in detail for a Maxwellian viscoelastic model of the turbulent stress in an accretion disc. This generalizes the conventional alpha viscosity model to account for the non-zero relaxation time of the turbulence, and is physically motivated by a consideration of the nature of magnetohydrodynamic turbulence. It is confirmed that circular discs are typically viscously unstable to eccentric perturbations, as found by Lyubarskij, Postnov & Prokhorov, if the conventional alpha viscosity model is adopted. However, the instability can usually be suppressed by introducing a sufficient relaxation time and/or bulk viscosity. It is then shown that an initially uniformly eccentric disc does not retain its eccentricity as had been suggested by previous analyses. The evolutionary equations should be useful in many applications, including understanding the origin of planetary eccentricities and testing theories of quasi-periodic oscillations in X-ray binaries.     

Marymia: an Archean, amphibolite facies-hosted, orogenic lode-gold deposit overprinted by Palaeoproterozoic orogenesis and base metal mineralisation, Western Australia

The Marymia gold deposit, comprising two orebodies, Keillor 1 and Keillor 2, is at the northern end of the Plutonic Well greenstone belt in the Marymia Inlier, in the southern Capricorn Orogen, just north of the Yilgarn craton. The Marymia Inlier is a discrete fault-bounded Archean gneiss-granitoid-greenstone domain surrounded by sedimentary basins that were formed and variably metamorphosed and deformed during several Palaeoproterozoic orogenic cycles. The greenstone sequence at Marymia is stratigraphically and geochemically similar to greenstone sequences in the Yilgarn craton, but was subjected to further deformation and metamorphism in the Palaeoproterozoic. Late Archean deformation (D1-D2) was ductile to brittle-ductile in style, whereas Palaeoproterozoic deformation was predominantly brittle. Equilibrium mineral assemblages indicate that peak amphibolite-facies metamorphism (540-575 °C, <3 kb) was overprinted by greenschist-facies metamorphism (300-360 °C). Petrographic textures indicate that prograde metamorphism was coeval with D1-D2, with peak metamorphism early to syn D2. Gold mineralisation at Marymia is hosted in metamorphosed tholeiitic basalts and banded iron formation. On a gross scale, the distribution of gold is controlled by D2 folds and shear zones. Lithological contacts with strong rheological or chemical contrasts provide local controls. Gold-related alteration comprises subtle millimetre- to centimetre-wide zones of silicification with variable amounts of quartz, hornblende, biotite, K-feldspar, plagioclase, calcite/siderite, scheelite, titanite, epidote, sulfide and telluride minerals. Quartz veins are generally narrow and discontinuous with low total volume of quartz. Gold is sited in the wall rock, at vein salvedges or within stringers of wall rock within veins. There are two distinct opaque-mineral assemblages: pyrite-pyrrhotite-chalcopyrite-galena and hessite-petzite-altaite-Bi-telluride-galena. Ore samples are variably enriched in Ag, Te, Pb, W, Cu, S and Fe reflecting heterogeneity of the ore mineralogy. Structural timing and temperature of formation of alteration and ore minerals support deposition of gold during late peak amphibolite-facies metamorphism from neutral to alkaline (pH=5-6), moderately oxidising (log P_O2,-21-22) and CO₂-bearing (X_CO2 Ƹ.2) fluids. The total sulfur content of the fluid is estimated at 1mDS. Lead isotope compositions support derivation of lead from within the local greenstone sequence. Gold lodes were deformed by faults and shear zones in the Palaeoproterozoic, with only limited remobilisation. Subeconomic, carbonate vein- and breccia-hosted base metal mineralisation is locally hosted within Palaeoproterozoic fault zones, which clearly cut gold lodes. Base-metal-related alteration is characterised by intense carbonatisation, chloritisation, and albitisation of the mafic host rocks. Mineral assemblages are consistent with formation at greenschist facies conditions. Lead isotope compositions support crystallisation at ca. 1.7 Ga from lead that is similar in composition to earlier gold-related galena.     

Electrical and electromagnetic surveys to locate possible causes of water seepage to ground surface at a quarry open pit near Helwan city,Egypt

Water seepage to ground surface at a limestone quarry located at Wadi Garawy about 20 km south-east of Helwan city in Egypt posed a real threat to the mining activity at the quarry. The quarry area is known to be very dry for decades and away from water utilities and infrastructures that may cause water leaks to the quarry. Geophysical investigation including 1D Vertical Electrical Sounding (VES), 2D Electrical Resistivity Tomography (ERT) and 1D Transient Electromagnetic (TEM) surveys were conducted to characterize the rock sequence and locate what could be a possible source of water seepage to the quarry. The resistivity profiles generated from the VES and TEM surveys mapped the rock units in the area down to depths exceeded 100 m. The ERT profiles acquired from the quarrying zone close to the water seepage spot have imaged the top of groundwater level at few meters below the ground surface at the quarry open pit. The spot of groundwater seepage seemed to occur at an area of limestone dissolution that were filled by finer sediments. The finer sediments acted as a hydrological conduit that allowed an upward seepage of groundwater to ground surface under the capillary action effect.     

Subpollen Particles as Atmospheric Cloud Condensation Nuclei

Izvestiya, Atmospheric and Oceanic Physics - Bioparticles constitute a significant fraction of atmospheric aerosol. Their size range varies from nanometers (macromolecules) to hundreds of...