Using a homogenous sample of 1962 quasars with redshift 3.0≤z≲4.5 drawn from the Sloan Digital Sky Survey (SDSS), we study the relationships between radio loudness, virial black hole
(BH) mass and Eddington ratio (accretion rate relative to the Eddington limit). For the radio-detected objects, we find a
significant (>99.5 per cent) anticorrelation between radio loudness R parameter and BH mass, consistent with previous studies of low-redshift radio-loud quasars. The truly radio-loud quasars
(R>30) are found to be confined to MBH≲1010 M⊙ within our sample. We also find that R is only weakly correlated with Eddington ratio Lbol/LEdd. Combined with previous results on the low-redshift R−Lbol/LEdd relation, this result indicates no strong Lbol/LEdd dependence of R at Lbol/LEdd≳10−2. On the other hand, the large scatter in these relationships suggests that other physical properties such as BH spin and
quasar clustering must also play an important role in quasar radio emission. 相似文献
Channel morphology and bed sediment erodibility are two crucial factors that significantly affect debris flow entrainment processes. Current debris flow entrainment models mostly hypothesize the erodible beds are infinite with uniform slopes. In this study, a series of small-scale flume experiments were conducted to investigate the effects of bed longitudinal inflexion and sediment porosity on basal entrainment characteristics. Experimental observations revealed that sediment entrainment is negligible at early stages and accelerates rapidly as several erosion points appear. Continual evolution of flow-bed interfaces changes interactions between debris flows and bed sediments, rendering the interfacial shear action involved into a mixed shear and frontal collisional action. Lower bed sediment porosity will change the spatial arrangement and orientation of particle mixture, strengthen the interlocking and anti-slide forces of adjacent sediment particles, and promote the formation of particle clusters, all of which will increase bed sediment resistance to erosion. By examining the post-experimental bed morphology, the slope-cutting amounts and topographic reliefs are determined to positively correlate with longitudinal transition angles. These high topographic reliefs may indicate the propensity of triangular slab erosion, rather than strip-shaped slab erosion, in non-uniform channels with relatively steep erodible beds. Empirical formulas are obtained that denote the relationships among bed sediment strength, channel curvature radius, and sediment porosity through a multi-parameter regression analysis. This study may aid in clarifying the complex coupling effects of spatial variations in debris flow dynamics as well as sediment erodibility and bed morphology in non-uniform channels with abundant seismic loose material.
The present study attempts to predict the reservoir sedimentation in 32 km region of the Tenryu River between the Hiraoka and Sakuma Dams in Japan. For numerical simulations of the reservoir sedimentation, the one-dimensional model of the Hydrologic Engineering Centre-River Analysis System (HEC-RAS) is used together with the inclusion of channel geometry, bed gradation curve, Exner-5 bed sorting mechanisms, fall velocity of the particle, and flow and sediment boundary conditions pertaining to modeling region. The modeling region of the Tenryu River is divided into 48 river stations with 47 reaches in the numerical simulations. The numerical model is calibrated using the available data for 48 years from 1957 to 2004. The formulae of sediment transport function, Manning’s roughness coefficient, computational increment and fall velocity have been identified for getting the best estimation of the Sakuma Dam reservoir sedimentation. Combination of obtained sensitive parameters and erodible limits of 2 m gave the best comparison with the measured bed profile. The computed results follow the trend of measured data with a small underestimation. Although Manning’s roughness coefficient has an effect on the sedimentation, no direct relation is found between the Manning’s roughness coefficient and reservoir sedimentation. It is found that the temperature of water has no effect on the reservoir sedimentation. 相似文献
Patterns in species geographic range size are relatively well-known for vertebrates,but still poorly known for plants.Contrasts of these patterns between groups have rarely been investigated.With a detailed flora and fauna distribution database of Xinjiang,China,we used regression methods,redundancy analysis and random forests to explore the relationship of environment and body size with the geographic range size of plants,mammals and birds in Xinjiang and contrast these patterns between plants and animals.We found positive correlations between species range size and body size.The range size of plants was more influenced by water variables,while that of mammals and birds was largely influenced by temperature variables.The productivity variable,i.e.,Enhanced Vegetation Index(EVI)was far more correlated with range size than climatic variables for both plants and animals,suggesting that vegetation productivity inferred from remote sensing data may be a good predictor of species range size for both plants and animals. 相似文献
