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21.
Digital elevation models (DEMs) at different resolutions (180, 360, and 720 m) are used to examine the impact of different levels of landscape representation on the hydrological response of a 690‐km2 catchment in southern Quebec. Frequency distributions of local slope, plan curvature, and drainage area are calculated for each grid size resolution. This landscape analysis reveals that DEM grid size significantly affects computed topographic attributes, which in turn explains some of the differences in the hydrological simulations. The simulations that are then carried out, using a coupled, process‐based model of surface and subsurface flow, examine the effects of grid size on both the integrated response of the catchment (discharge at the main outlet and at two internal points) and the distributed response (water table depth, surface saturation, and soil water storage). The results indicate that discharge volumes increase as the DEM is coarsened, and that coarser DEMs are also wetter overall in terms of water table depth and soil water storage. The reasons for these trends include an increase in the total drainage area of the catchment for larger DEM cell sizes, due to aggregation effects at the boundary cells of the catchment, and to a decrease in local slope and plan curvature variations, which in turn limits the capacity of the watershed to transmit water downslope and laterally. The results obtained also show that grid resolution effects are less pronounced during dry periods when soil moisture dynamics are mostly controlled by vertical fluxes of evaporation and percolation. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
22.
Landslides - Rockslide-debris flow may cause catastrophic damages because of its high speed and long run-out distance. The influences of slope gradient and gully channel on the entrainment,... 相似文献
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24.
Andrea Merloni Sebastian Heinz Tiziana Di Matteo 《Astrophysics and Space Science》2005,300(1-3):45-53
We examine the disc-jet connection in stellar mass and supermassive black holes by investigating the properties of their compact
emission in the hard X-ray and radio bands. We compile a sample of ∼100 active galactic nuclei with measured mass, 5 GHz core
emission, and 2–10 keV luminosity, together with eight galactic black holes with a total of ∼50 simultaneous observations
in the radio and X-ray bands. Using this sample, we study the correlations between the radio (LR) and the X-ray (LX) luminosity and the black hole mass (M). We find that the radio luminosity is correlated with both M and LX, at a highly significant level. We show how this result can be used to extend the standard unification by orientation scheme
to encompass unification by mass and accretion rate. 相似文献
25.
A Fundamental Plane of black hole activity 总被引:1,自引:0,他引:1
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27.
The higher-order scalar concentration fluctuation properties are examined in the context of Monin–Obukhov similarity theory
for a variety of greenhouse gases that have distinct and separate source/sink locations along an otherwise ideal micrometeorological
field site. Air temperature and concentrations of water vapour, carbon dioxide and methane were measured at high frequency
(10 Hz) above a flat and extensive peat-land soil in the San Joaquin–Sacramento Delta (California, USA) area, subjected to
year-round grazing by beef cattle. Because of the heterogeneous distribution of the sources and sinks of CO2 and especially CH4 emitted by cattle, the scaling behaviour of the higher-order statistical properties diverged from predictions based on a
balance between their production and dissipation rate terms, which can obtained for temperature and H2O during stationary conditions. We identify and label these departures as ‘exogenous’ because they depend on heterogeneities
and non-stationarities induced by boundary conditions on the flow. Spectral analysis revealed that the exogenous effects show
their signatures in regions with frequencies lower than those associated with scalar vertical transport by turbulence, though
the two regions may partially overlap in some cases. Cospectra of vertical fluxes appear less influenced by these exogenous
effects because of the modulating role of the vertical velocity at low frequencies. Finally, under certain conditions, the
presence of such exogenous factors in higher-order scalar fluctuation statistics may be ‘fingerprinted’ by a large storage
term in the mean scalar budget. 相似文献
28.
Despite their importance for pollutant dispersion in urban areas, the special features of dispersion at street intersections
are rarely taken into account by operational air quality models. Several previous studies have demonstrated the complex flow
patterns that occur at street intersections, even with simple geometry. This study presents results from wind-tunnel experiments
on a reduced scale model of a complex but realistic urban intersection, located in central London. Tracer concentration measurements
were used to derive three-dimensional maps of the concentration field within the intersection. In combination with a previous
study (Carpentieri et al., Boundary-Layer Meteorol 133:277–296, 2009) where the velocity field was measured in the same model,
a methodology for the calculation of the mean tracer flux balance at the intersection was developed and applied. The calculation
highlighted several limitations of current state-of-the-art canyon dispersion models, arising mainly from the complex geometry
of the intersection. Despite its limitations, the proposed methodology could be further developed in order to derive, assess
and implement street intersection dispersion models for complex urban areas. 相似文献
29.
Matteo Guainazzi 《Astrophysics and Space Science》2009,320(1-3):129-134
I briefly review in this paper the main observational properties of relativistically broadened X-ray spectral lines in Galactic Black Holes and Active Galactic Nuclei, and the (scanty) estimates of their frequency in the corresponding parent populations. The available measurements allow us to derive some constraints on the black hole spin and mass, and on the accretion disk geometry and illumination. 相似文献
30.
Matteo Barnabè Carlo Nipoti Léon V. E. Koopmans Simona Vegetti Luca Ciotti 《Monthly notices of the Royal Astronomical Society》2009,393(4):1114-1126
We apply the joint lensing and dynamics code for the analysis of early-type galaxies, 'Combined Algorithm for Unified Lensing and Dynamics ReconstructiON ( cauldron )', to a rotating N -body stellar system with dark matter halo which significantly violates the two major assumptions of the method, i.e. axial symmetry supported by a two-integral distribution function. The goal is to study how cauldron performs in an extreme case, and to determine which galaxy properties can still be robustly recovered. Three data sets, corresponding to orthogonal lines of sight, are generated from the N -body system and analysed with the identical procedure followed in the study of real lens galaxies, adopting an axisymmetric power-law total density distribution. We find that several global properties of the N -body system are recovered with remarkable accuracy, despite the fact that the adopted power-law model is too simple to account for the lack of symmetry of the true density distribution. In particular, the logarithmic slope of the total density distribution is robustly recovered to within less than 10 per cent (with the exception of the ill-constrained very inner regions), the inferred angle-averaged radial profile of the total mass closely follows the true distribution, and the dark matter fraction of the system (inside the effective radius) is correctly determined within ∼10 per cent of the total mass. Unless the line-of-sight direction is almost parallel to the total angular momentum vector of the system, reliably recovered quantities also include the angular momentum, the V /σ ratio and the anisotropy parameter δ. We conclude that the cauldron code can be safely and effectively applied to real early-type lens galaxies, also providing reliable information for the systems that depart significantly from the method's assumptions. 相似文献