69,050 research outputs found
Probing ~100 AU Intergalactic MgII Absorbing "Cloudlets" with Quasar Microlensing
Intergalactic MgII absorbers are known to have structures down to scales ~
10^{2.5} pc, and there are now indications that they may be fragmented on
scales <~ 10^{-2.5} pc (Hao et al., astro-ph/0612409). When a lensed quasar is
microlensed, the micro-images of the quasar experience creation, destruction,
distortion, and drastic astrometric changes during caustic-crossing. I show
that quasar microlensing can effectively probe MgII and other absorption
"cloudlets" with sizes ~ 10^{-4.0} - 10^{-2.0} pc by inducing significant
spectral variability on the timescales of months to years. With numerical
simulations, I demonstrate the feasibility of applying this method to
Q2237+0305, and I show that high-resolution spectra of this quasar in the near
future would provide a clear test of the existence of such metal-line
absorption "cloudlets" along the quasar sight line.Comment: 13 pages, 2 figures, ApJ, submitted; for PDF file with high-res
figures, see http://www.astronomy.ohio-state.edu/~dong/mg2/mg2.pd
Crystal structure of Schmallenberg orthobunyavirus nucleoprotein-RNA complex reveals a novel RNA sequestration mechanism
Schmallenberg virus (SBV) is a newly emerged orthobunyavirus (family Bunyaviridae) that has caused severe disease in the offspring of farm animals across Europe. Like all orthobunyaviruses, SBV contains a tripartite negative-sense RNA genome that is encapsidated by the viral nucleocapsid (N) protein in the form of a ribonucleoprotein complex (RNP). We recently reported the three-dimensional structure of SBV N that revealed a novel fold. Here we report the crystal structure of the SBV N protein in complex with a 42-nt-long RNA to 2.16 Ă
resolution. The complex comprises a tetramer of N that encapsidates the RNA as a cross-shape inside the protein ring structure, with each protomer bound to 11 ribonucleotides. Eight bases are bound in the positively charged cleft between the N- and C-terminal domains of N, and three bases are shielded by the extended N-terminal arm. SBV N appears to sequester RNA using a different mechanism compared with the nucleoproteins of other negative-sense RNA viruses. Furthermore, the structure suggests that RNA binding results in conformational changes of some residues in the RNA-binding cleft and the N- and C-terminal arms. Our results provide new insights into the novel mechanism of RNA encapsidation by orthobunyaviruses
Single Image Super-Resolution Using Multi-Scale Convolutional Neural Network
Methods based on convolutional neural network (CNN) have demonstrated
tremendous improvements on single image super-resolution. However, the previous
methods mainly restore images from one single area in the low resolution (LR)
input, which limits the flexibility of models to infer various scales of
details for high resolution (HR) output. Moreover, most of them train a
specific model for each up-scale factor. In this paper, we propose a
multi-scale super resolution (MSSR) network. Our network consists of
multi-scale paths to make the HR inference, which can learn to synthesize
features from different scales. This property helps reconstruct various kinds
of regions in HR images. In addition, only one single model is needed for
multiple up-scale factors, which is more efficient without loss of restoration
quality. Experiments on four public datasets demonstrate that the proposed
method achieved state-of-the-art performance with fast speed
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