Limits on luminosity and mass accretion rate of a radiation pressure dominated accretion disc

There is a maximum for the gravity of a black hole in the vertical direction in the accretion disc. Outflows may probably be driven from the disc if the radiation flux of the disc is greater than a critical value corresponding to the maximal vertical gravity. We find that outflows are driven by the radiation force from the disc if the accretion rate is greater than the Eddington rate. The radiation of the disc is therefore limited by such outflows. The disc luminosity, L=L_Edd\propto ln mdot, at large-mdot cases. The Eddington ratio of the disc is ~3 for mdot~100, which is significantly lower than that of a conventional slim disc without outflows. This implies that the emission from some ultra-luminous X-ray sources with highly super Eddington luminosity should be Doppler beamed, or intermediate mass black holes are in these sources instead of stellar mass black holes. The spectra of the discs with outflows are saturated in the high frequency end provided mdot>2. We suggest that the saturated emission can be observed to estimate the masses of the black holes accreting at high rates, such as the narrow-line Seyfert galaxies, with the model calculations. The rate of the mass accreted by the black hole is always around the Eddington rate even if the mass accretion rate at the outer radius is very high, because most of the gas is removed into the outflows. This implies that the luminous quasars at high redshifts z>6 should have grown up through persistent accretion at a rate close to the Eddington rate.Comment: 8 pages, accepted by MNRA

Star Formation Properties in Barred Galaxies(SFB). III. Statistical Study of Bar-driven Secular Evolution using a sample of nearby barred spirals

Stellar bars are important internal drivers of secular evolution in disk galaxies. Using a sample of nearby spiral galaxies with weak and strong bars, we explore the relationships between the star formation feature and stellar bars in galaxies. We find that galaxies with weak bars tend to be coincide with low concentrical star formation activity, while those with strong bars show a large scatter in the distribution of star formation activity. We find enhanced star formation activity in bulges towards stronger bars, although not predominantly, consistent with previous studies. Our results suggest that different stages of the secular process and many other factors may contribute to the complexity of the secular evolution. In addition, barred galaxies with intense star formation in bars tend to have active star formation in their bulges and disks, and bulges have higher star formation densities than bars and disks, indicating the evolutionary effects of bars. We then derived a possible criterion to quantify the different stages of bar-driven physical process, while future work is needed because of the uncertainties.Comment: 30 single-column pages, 9 figures, accepted for publication in A

The Impact of MOOCs on College English Reform in Mainland China

Massive Open Online Courses (MOOCs) are internationally accepted as a popular online learning, its introduction into Mainland China provides an opportunity for College English education reform, which is on progress since 2007. This article attempts to draw a picture of College English teaching reform under the influence of MOOCs by adopting documentary research method through analyzing all the essays about College English teaching under the wave of MOOCs in CNKI (China National Knowledge Infrastructure) according to their research contents. The data collected shows that theoretically College English teaching could be reformed by taking the form of MOOCs in the courses of English for general purposes (EGP), English for general education (EGE), and English for specific purposes (ESP). It seems that during the reform teaching models and student-teacher relationship are altered by the MOOCs environment. Additionally, College English courses on several MOOCs platforms are analyzed, they further prove the practical College English courses done on MOOCs platforms. This paper seems to throw light on a general overview of College English teaching in Mainland China for English teachers and researchers and propose further improvement for college English teaching reform

Limitations of RNA interference as a potential technique for crop protection against insect pests

The RNAi response suppresses gene expression at the post-transcriptional level and the potential of this technique to give control of insect pests in crops has been recognised for a decade. This project focuses on a comparison of RNAi responses in insects of different orders by injecting and feeding dsRNA directed against thread (APIN) and V-Type- ATPase E homologues in the target species. The results showed systemic RNAi responses, and mortality, occurred in larvae of the Tribolium castaneum (T. castaneum), Coleopteran, but not a Hemipteran, the Acyrthosiphon pisum (A. pisum), where comparatively low levels of gene down-regulation were only achieved by injection of dsRNA. DsRNA injection produced both a lethal phenotype and gene down- regulation in larvae of the dipteran species Musca domestica (M. domestica), and Delia radicum (D. radicum), although the effects were found to be stage dependent. Rapid dsRNA degradation in the extracellular environment could lead to a limitation of RNAi reponses. In vitro experiments show that dsRNA was degraded rapidly by A. pisum haemolymph and gut extracts, and less rapidly by D. radicum larval extracts. However, T. castaneum larval extracts differ in both the amount and qualitative nature of their RNase activity; dsRNA was degraded at a slow rate, predominantly by exonuclease activity rather than endonuclease activity. A strategy using recombinant proteins was used to address limitations of RNAi effects after feeding dsRNA in insects. A recombinant protein containing an RNA binding domain (RBD) was selected to conjugate dsRNA forming a protein-RNA complex. The complexed protein enhanced the stability of dsRNA and protected it from degradation from insect extracts. A fusion protein containing snowdrop lectin (GNA) linked to RBD was also developed to produce a "systemic" RNAi effect, by transporting the protein-RNA complex to the insect haemolymph using the lectin as a "carrier"

An Analysis of Phonics Teaching in Mainland China

This article tries to analyze the present status of phonics teaching in Mainland China by using documentary research method through sorting out all the essays about phonics teaching in CNKI (China National Knowledge Infrastructure) according to their research contents and research methods. The data collected shows that Phonics, Pinyin and IPA are mainly discussed topics, especially different roles of them in English teaching. Unfortunately, misconceptions about phonics do appear in some of those essays collected, while localization of phonics is emerging. This paper seems to shed light on a general overview of English phonics teaching in Mainland China for English teachers and researchers and cope up with the difficult points and conflicts to provide improvement for phonics teaching