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Andrew M. Read Ian R. Stevens 《Monthly notices of the Royal Astronomical Society》2002,335(1):L36-L40
We present results from XMM–Newton Reflection Grating Spectrometer observations of the prototypical starburst galaxy M82. These high-resolution spectra represent the best X-ray spectra to date of a starburst galaxy. A complex array of lines from species over a wide range of temperatures is seen, the most prominent being due to Lyman α emission from abundant low- Z elements such as N, O, Ne, Mg and Si. Emission lines from helium-like charge states of the same elements are also seen in emission, as are strong lines from the entire Fe L series. Further, the O vii line complex is resolved and is seen to be consistent with gas in collisional ionization equilibrium.
Spectral fitting indicates emission from a large mass of gas with a differential emission measure over a range of temperatures (from ∼ 0.2 to ∼ 1.6 keV, peaking at ∼ 0.7 keV), and evidence for super-solar abundances of several elements is indicated. Spatial analysis of the data indicates that low-energy emission is more extended to the south and east of the nucleus than to the north and west. Higher energy emission is far more centrally concentrated. 相似文献
Spectral fitting indicates emission from a large mass of gas with a differential emission measure over a range of temperatures (from ∼ 0.2 to ∼ 1.6 keV, peaking at ∼ 0.7 keV), and evidence for super-solar abundances of several elements is indicated. Spatial analysis of the data indicates that low-energy emission is more extended to the south and east of the nucleus than to the north and west. Higher energy emission is far more centrally concentrated. 相似文献
965.
Modern ideas of thermomechanics are used to develop families of models describing the elastic/plastic behaviour of cohesionless soils deforming under triaxial conditions. Once the form of the free energy and dissipation potential functions have been specified, the corresponding yield loci, flow rules, isotropic and kinematic hardening rules as well as the elasticity law are deduced in a systematic manner. The families contain the classical linear frictional (Coulomb type) models and the classical critical state models as special cases. The generalized models discussed here include non‐associated flow rules, shear as well as volumetric hardening, anisotropic responses and rotational yield loci. The various parameters needed to describe the models can be interpreted in terms of ratio of the plastic work, which is dissipated, to that which is stored. Non‐associated behaviour is found to occur whenever this division between dissipated and stored work is not equal. Micro‐level interpretations of stored plastic work are discussed. The models automatically satisfy the laws of thermodynamics, and there is no need to invoke any stability postulates. Some classical forms of the peak‐strength/dilatancy relationship are established theoretically. Some representative drained and undrained paths are computed. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
966.
Roberto De Propris Matthew Colless John A. Peacock Warrick J. Couch Simon P. Driver Michael L. Balogh Ivan K. Baldry Carlton M. Baugh Joss Bland-Hawthorn Terry Bridges Russell Cannon Shaun Cole Chris Collins Nicholas Cross Gavin Dalton George Efstathiou Richard S. Ellis Carlos S. Frenk Karl Glazebrook Edward Hawkins Carole Jackson Ofer Lahav Ian Lewis Stuart Lumsden Steve Maddox Darren Madgwick Peder Norberg Will Percival Bruce A. Peterson Will Sutherland Keith Taylor 《Monthly notices of the Royal Astronomical Society》2004,351(1):125-132
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Lucy A. McKergow Ian P. Prosser David M. Weaver Rodger B. Grayson Adrian E. G. Reed 《水文研究》2006,20(11):2327-2346
Declining water quality on the south coast of Western Australia has been linked to current agricultural practices. Riparian buffers were identified as a tool available to farmers and catchment managers to achieve water quality improvements. This study compares 10 m wide regenerating grass and Eucalyptus globulus buffer performance. Surface and subsurface water quality were monitored over a 3‐year period. Nutrient and sediment transport were both dominated by subsurface flow, in particular through the B‐horizon, and this may seriously limit the surface‐runoff‐related functions of the riparian buffers. Riparian buffer trapping efficiencies were variable on an event basis and annual basis. The grass buffer reduced total phosphorus, filterable reactive phosphorus, total nitrogen and suspended sediment loads from surface runoff by 50 to 60%. The E. globulus buffer was not as effective, and total load reductions in surface runoff ranged between 10 and 40%. A key difference between the grass and E. globulus buffers was the seasonality of sediment and nutrient transport. Surface runoff, and therefore sediment and nutrient transport, occurred throughout the year in the E. globulus buffer, but only during the winter in the grass buffer. As a consequence of high summer nutrient and sediment concentrations, half the annual loads moving via surface runoff pathways through the E. globulus buffer were transported during intense summer storms. This study demonstrates that grass and E. globulus riparian buffers receiving runoff from pasture under natural rainfall can reduce sediment and nutrient loads from surface runoff. However, in this environment the B‐horizon subsurface flow is the dominant flowpath for nutrient transport through the riparian buffers, and this subsurface flow pathway carries contaminant loads at least three times greater than surface runoff. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
969.
Ian D. Howarth Richard J. Price Ian A. Crawford Isabel Hawkins 《Monthly notices of the Royal Astronomical Society》2002,335(2):267-274
We present observations of the Li i 6708 Å doublet in the ζ Oph sightline, obtained at a resolution of ∼106 and a signal-to-noise ratio of ∼1200, together with supplementary observations of K i λ 7699 and the Na i λ 3302 doublet. These observations marginally resolve the main '−15 km s−1 ' system into its two principal clouds; we model the data using standard physical assumptions, but in a statistically rigorous manner, taking fully into account the hyperfine, doublet and isotopic structure for each species, in each cloud, using a new code, vapid . The average 7 Li/6 Li ratio determined in this sightline is 1.12±0.20 dex (68 per cent confidence interval), in excellent agreement with the solar-system (meteoritic) value. The ratios in the individual clouds are determined with less precision, but are also consistent with the solar-system value, as is the total lithium abundance (with little evidence for depletion). The thermal and 'turbulent' broadening in the two clouds is discussed on the basis of observed line widths. 相似文献
970.