1,685 research outputs found
Estimate black hole masses of AGNs using ultraviolet emission line properties
Based on the measured sizes of broad line region of the reverberation-mapping
AGN sample, two new empirical relations are introduced to estimate the central
black hole masses of radio-loud high-redshift () AGNs. First, using
the archival spectroscopy data at UV band for the
reverberation-mapping objects, we obtained two new empirical relations between
the BLR size and \Mg/\C emission line luminosity. Secondly, using the newly
determined black hole masses of the reverberation-mapping sample for
calibration, two new relationships for determination of black hole mass with
the full width of half maximum and the luminosity of \Mg/\C line are also
found. We then apply the relations to estimate the black hole masses of AGNs in
Large Bright Quasar Surveyq and a sample of radio-loud quasars. For the objects
with small radio-loudness, the black hole mass estimated using the R_{\rm BLR}
- L_{\eMg/\eC} relation is consistent with that from the relation. But for radio-loud AGNs, the mass estimated
from the R_{BLR} - L_{\eMg/\eC} relation is systematically lower than that
from the continuum luminosity . Because jets could have
significant contributions to the UV/optical continuum luminosity of radio-loud
AGNs, we emphasized again that for radio-loud AGNs, the emission line
luminosity may be a better tracer of the ionizing luminosity than the continuum
luminosity, so that the relations between the BLR size and UV emission line
luminosity should be used to estimate the black hole masses of high redshift
radio-loud AGNs.Comment: 19 pages, 10 figure
Effect of Grazing on Soil Carbon and Nitrogen in Alpine Madow, Eastern of Tibetan Plateau
As the grassland ecosystem in the Tibetan Plateau is very fragile, overgrazing likely leads to more serious damages to it than other ecosystems. In the past 30 years, 37% of the alpine meadows have been heavily damaged by grazing causing degradation of native vegetation, a decline in species richness and feed value, and more seriously soil erosion (Six et al. 2004). The impact of grazing on alpine grasslands appears to be hysteresis, as the soil needs more time to recover than the vegetation. So analysing the effect of grazing intensity on soil characteristics is an important way to reveal how grazing influenced grassland ecosystem. Although much research about grazing effects on nutrients, immobilization of carbon (C) and nitrogen (N) in soils and soil microbes have been done in different terrestrial environments, similar effort has rarely focused on the Tibetan Plateau. In this study, soil organic carbon (SOC) and total nitrogen (STN) in 0-30 cm soil depth were measured in the alpine meadow at the northeastern margin of the Tibetan Plateau, to determine suitable grazing intensity from the viewpoints of soil health and fertility, and providing a scientific basis for guiding the reasonable use of the alpine meadow
High-resolution modeling of typhoon morakot (2009): Vortex rossby waves and their role in extreme precipitation over Taiwan
A high-resolution nonhydrostatic numerical model, the Advanced Regional Prediction System (ARPS), was used to simulate Typhoon Morakot (2009) as it made landfall over Taiwan, producing record rainfall totals. In particular, the mesoscale structure of the typhoon was investigated, emphasizing its associated deep convection, the development of inner rainbands near the center, and the resultant intense rainfall over western Taiwan. Simulations at 15- and 3-km grid spacing revealed that, following the decay of the initial inner eyewall, a new, much larger eyewall developed as the typhoon made landfall over Taiwan. Relatively large-amplitude wave structures developed in the outer eyewall and are identified as vortex Rossby waves (VRWs), based on the wave characteristics and their similarity to VRWs identified in previous studies. Moderate to strong vertical shear over the typhoon system produced a persistent wavenumber-1 (WN1) asymmetric structure during the landfall period, with upward motion and deep convection in the downshear and downshear-left sides, consistent with earlier studies. This strong asymmetry masks the effects of WN1 VRWs. WN2 and WN3 VRWs apparently are associated with the development of deep convective bands in Morakot's southwestern quadrant. This occurs as the waves move cyclonically into the downshear side of the cyclone. Although the typhoon track and topographic enhancement contribute most to the recordbreaking rainfall totals, the location of the convective bands, and their interaction with the mountainous terrain of Taiwan, also affect the rainfall distribution. Quantitatively, the 3-km ARPS rainfall forecasts are superior to those obtained from coarser-resolution models. © 2013 American Meteorological Society
The black hole fundamental plane from a uniform sample of radio and X-ray emitting broad line AGNs
We derived the black hole fundamental plane relationship among the 1.4GHz
radio luminosity (L_r), 0.1-2.4keV X-ray luminosity (L_X), and black hole mass
(M) from a uniform broad line SDSS AGN sample including both radio loud and
radio quiet X-ray emitting sources. We found in our sample that the fundamental
plane relation has a very weak dependence on the black hole mass, and a tight
correlation also exists between the Eddington luminosity scaled X-ray and radio
luminosities for the radio quiet subsample. Additionally, we noticed that the
radio quiet and radio loud AGNs have different power-law slopes in the
radio--X-ray non-linear relationship. The radio loud sample displays a slope of
1.39, which seems consistent with the jet dominated X-ray model. However, it
may also be partly due to the relativistic beaming effect. For radio quiet
sample the slope of the radio--X-ray relationship is about 0.85, which is
possibly consistent with the theoretical prediction from the accretion flow
dominated X-ray model. We briefly discuss the reason why our derived
relationship is different from some previous works and expect the future
spectral studies in radio and X-ray bands on individual sources in our sample
to confirm our result.Comment: 23 pages, 7 figures, ApJ accepte
Surface Work Function of Transparent Conductive ZnO Films
AbstractThe influence of Al doped on work function of ZnO thin film with C-axis preferred orientation were analyzed both theoretically and experimentally. Pure ZnO and Al-doped ZnO(ZnO:Al) films were deposited on n-type Si substrate by radio frequency (RF) magnetron sputtering. Surface work function were calculated using the first-principles with pseudopotential method based on density-functional theory (DFT) of ZnO and ZnO:Al surface structure. It was found that the theoretical value of work function of (002) plane ZnO and ZnO:Al were 5.076ev and 4.978ev respectively. Following I-V-T characteristics of the heterojunctions were investigated, the work function of ZnO and ZnO:Al were obtained at 4.71ev and 4.62ev, respectively. Al doped led to the value of work function reduced by 0.09ev, which was consistent with 0.098ev calculated by the first-principle algorithm
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