Online Estimation of Network Point Processes for Event Streams

A common goal in network modeling is to uncover the latent community structure present among nodes. For many real-world networks, the true connections consist of events arriving as streams, which are then aggregated to form edges, ignoring the dynamic temporal component. A natural way to take account of these temporal dynamics of interactions is to use point processes as the foundation of network models for community detection. Computational complexity hampers the scalability of such approaches to large sparse networks. To circumvent this challenge, we propose a fast online variational inference algorithm for estimating the latent structure underlying dynamic event arrivals on a network, using continuous-time point process latent network models. We describe this procedure for networks models capturing community structure. This structure can be learned as new events are observed on the network, updating the inferred community assignments. We investigate the theoretical properties of such an inference scheme, and provide regret bounds on the loss function of this procedure. The proposed inference procedure is then thoroughly compared, using both simulation studies and real data, to non-online variants. We demonstrate that online inference can obtain comparable performance, in terms of community recovery, to non-online variants, while realising computational gains. Our proposed inference framework can also be readily modified to incorporate other popular network structures.Comment: 45 page

Methanotrophic abundance and community fingerprint in pine and tea plantation soils as revealed by molecular methods

Understanding the community structure of methane-oxidizing bacteria (methanotrophs) is important to assess the microbial oxidation of the greenhouse gas methane (CH4) in soil under different land uses. Soil samples were collected from two plantation plots of pine and tea in southern China. Methanotrophic abundance was quantified with quantitative real-time polymerase chain reaction (qPCR) based on the 16S rRNA and pmoA genes, and the community fingerprint was characterized with denaturing gradient gel electrophoresis (DGGE) targeting the pmoA gene. No significant difference in the gene copy numbers of methanotrophs was found between the pine and tea land-use, regardless of 16S rRNA and pmoA genes. Higher abundance of type I (1.35 vs 1.66×108 copie g-1 soil) over type II methanotrophs (8.59 vs 10.9 × 107) were found both in pine and tea plantation soils. Apparent differences in methanotrophic community fingerprint were observed between the pine and tea treatments. Correlations analysis between methanotrophic abundance and soil characteristics, combining with canonial correspondence analysis (CCA) regarding community fingerprint and environmental parameters indicated that soil pH and available phosphorus were the most important factors potentially affecting the methanotrophic community diversity in the acidic red soil.Key words: Denaturing gradient gel electrophoresis (DGGE), land use, methanotrophs, pmoA gene, quantitative real-time PCR (qPCR)

Bis[1-(2,6-dichloro­benz­yl)-3-methyl­pyrazin-1-ium] bis­(maleonitrile­dithiol­ato)nickelate(II)

In the crystal structure of the title compound, (C12H11Cl2N2)2[Ni(C4N2S2)2], the NiII complex dianion is located on an inversion centre. The NiII atom is coordinated by four S atoms in a square-planar geometry. In the cation, the dihedral angle between the benzene and pyrazine rings is 85.2 (2)°

Spin-dependent gain and loss in photonic quantum spin Hall systems

Topological phases are greatly enriched by including non-Hermiticity. While most works focus on the topology of the eigenvalues and eigenstates, how topologically nontrivial non-Hermitian systems behave in dynamics has only drawn limited attention. Here, we consider a breathing honeycomb lattice known to emulate the quantum spin Hall effect and exhibits higher-order corner modes. We find that non-reciprocal intracell couplings introduce gain in one pseudo-spin subspace while loss with the same magnitude in the other. In addition, non-reciprocal intracell couplings can also suppress the spin mixture of the edge modes at the boundaries and delocalize the higher-order corner mode. Our findings deepen the understanding of non-Hermitian topological phases and bring in the spin degree of freedom in manipulating the dynamics in non-Hermitian systems.Comment: 17 pages, 5 figure

The Photometric System of Tsinghua-NAOC 80-cm Telescope at NAOC Xinglong Observatory

Tsinghua-NAOC (National Astronomical Observatories of China) Telescope (hereafter, TNT) is an 80-cm Cassegrain reflecting telescope located at Xinglong bservatory of NAOC, with main scientific goals of monitoring various transients in the universe such as supernovae, gamma-ray bursts, novae, variable stars, and active galactic nuclei. We present in this paper a systematic test and analysis of the photometric performance of this telescope. Based on the calibration observations on twelve photometric nights, spanning the period from year 2004 to year 2012, we derived an accurate transformation relationship between the instrumental $ubvri$ magnitudes and standard Johnson $UBV$ and Cousins $RI$ magnitudes. In particular, the color terms and the extinction coefficients of different passbands are well determined. With these data, we also obtained the limiting magnitudes and the photometric precision of TNT. It is worthwhile to point out that the sky background at Xinglong Observatory may become gradually worse over the period from year 2005 to year 2012 (e.g., $\sim$21.4 mag vs. $\sim$20.1 mag in the V band).Comment: 12 pages,9 figures, accepted by RA

Braiding topology of symmetry-protected degeneracy points in non-Hermitian systems

Degeneracy points in non-Hermitian systems are of great interest. While a framework exists for understanding their behavior in the absence of symmetry, it does not apply to symmetry-protected degeneracy points with reduced codimension. In this work, we investigate the braiding topology and non-abelian conservation rule of these symmetry-protected degenerate points. We find that, contrary to simple annihilation, pairwise created symmetry-protected degeneracy points merge into a higher order degeneracy point, which goes beyond the abelian picture. We verify these findings using a model Hamiltonian and full-wave simulations in an electric circuit system.Comment: 17 pages, 7 figure

An analysis of anxiety-related postings on sina weibo

This study examines anxiety-related postings on Sina Weibo to gain insight into social networking about mental health. The themes of a random sample of anxiety-related postings (n = 1000) were assessed. The disclosure of anxiety was the most common theme. The prevalence of anxiety was higher in certain areas where the economy is stronger than others, and the people living there suffered from more stress. Users who talked about feeling anxious tended to be more active on social media during leisure hours and less active during work hours. Our findings may be developed to detect and help individuals who may suffer from anxiety disorders at a low cost.The authors acknowledge the support from the Harbin Institute of Technology’s Visiting Scholar Program and the National Natural Science Foundation of China (grant no. 71531013)