Relativistic jet activity from the tidal disruption of a star by a massive black hole

Supermassive black holes have powerful gravitational fields with strong gradients that can destroy stars that get too close, producing a bright flare in ultraviolet and X-ray spectral regions from stellar debris that forms an accretion disk around the black hole. The aftermath of this process may have been seen several times over the past two decades in the form of sparsely sampled, slowly fading emission from distant galaxies, but the onset of the stellar disruption event has not hitherto been observed. Here we report observations of a bright X-ray flare from the extragalactic transient Swift J164449.3+573451. This source increased in brightness in the X-ray band by a factor of at least 10,000 since 1990 and by a factor of at least 100 since early 2010. We conclude that we have captured the onset of relativistic jet activity from a supermassive black hole. A companion paper comes to similar conclusions on the basis of radio observations. This event is probably due to the tidal disruption of a star falling into a supermassive black hole, but the detailed behaviour differs from current theoretical models of such events.     

Hesperomyces virescens (Fungi,Ascomycota, Laboulbeniales) attacking Harmonia axyridis (Coleoptera,Coccinellidae) in its native range

This study intended to find data on obligate ectoparasitic Laboulbeniales (Fungi, Ascomycota) on Chinese Harmonia axyridis (Coleoptera, Coccinellidae). After having screened over four thousand dried specimens of H. axyridis and close relatives, we present the first (historical) record of Chinese H. axyridis infected with Hesperomyces virescens. We suggest that H. virescens is a historically globally distributed species and hypothesize that (native) infection was lost when H. axyridis was introduced in North America.     

Characterization of low-purity clays for geopolymer binder formulation

The production of geopolymer binders from low-purity clays was investigated. Three low-purity clays were calcined at 750℃ for 4 h. The calcined clays were chemically activated by the alkaline solutions of NaOH and Na₂SiO₃. The compressive strength was measured as a function of curing time at room temperature and 85℃. The results were compared with those of a pure kaolin sample. An amorphous aluminosilicate polymer was formed in all binders at both processing temperatures. The results show that, the mechanical properties depend on the type and amount of active aluminum silicates in the starting clay material, the impurities, and the processing temperature.     

太赫兹振荡器件之间同相位锁定机制的研究

本文详细研究了平面纳米耿氏振荡器的耦合特性。研究表明：把两个器件直接并联组成阵列时,由于器件间的耦合较弱,两器件无法协同工作,因而输出信号随时间无规波动;为此我们通过在器件间引入额外的表面栅,利用栅极偏压增强耦合,使得器件工作处于基波相位锁定状态,从而输出幅度稳定、工作频率约为0.37 THz的信号。通过对器件沟道内部电子浓度的进一步分布分析,我们发现器件同相位锁定机制的微观实质为两沟道内部动力学偶极畴处于同步状态。由于双器件阵列的输出信号幅值为单器件的两倍,因此这种结构设计可以提升器件的输出功率。     

Sequence and analysis of chromosome 4 of the plant Arabidopsis thaliana

The higher plant Arabidopsis thaliana (Arabidopsis) is an important model for identifying plant genes and determining their function. To assist biological investigations and to define chromosome structure, a coordinated effort to sequence the Arabidopsis genome was initiated in late 1996. Here we report one of the first milestones of this project, the sequence of chromosome 4. Analysis of 17.38 megabases of unique sequence, representing about 17% of the genome, reveals 3,744 protein coding genes, 81 transfer RNAs and numerous repeat elements. Heterochromatic regions surrounding the putative centromere, which has not yet been completely sequenced, are characterized by an increased frequency of a variety of repeats, new repeats, reduced recombination, lowered gene density and lowered gene expression. Roughly 60% of the predicted protein-coding genes have been functionally characterized on the basis of their homology to known genes. Many genes encode predicted proteins that are homologous to human and Caenorhabditis elegans proteins.     

A gamma-ray burst with a high-energy spectral component inconsistent with the synchrotron shock model

Gamma-ray bursts are among the most powerful events in nature. These events release most of their energy as photons with energies in the range from 30 keV to a few MeV, with a smaller fraction of the energy radiated in radio, optical, and soft X-ray afterglows. The data are in general agreement with a relativistic shock model, where the prompt and afterglow emissions correspond to synchrotron radiation from shock-accelerated electrons. Here we report an observation of a high-energy (multi-MeV) spectral component in the burst of 17 October 1994 that is distinct from the previously observed lower-energy gamma-ray component. The flux of the high-energy component decays more slowly and its fluence is greater than the lower-energy component; it is described by a power law of differential photon number index approximately -1 up to about 200 MeV. This observation is difficult to explain with the standard synchrotron shock model, suggesting the presence of new phenomena such as a different non-thermal electron process, or the interaction of relativistic protons with photons at the source.     

Sample Size Dependence of Second Magnetization Peak in Type－II Superconductors

We show that the second magnetization peak (SMP), i. e., an increase in the magnetization hysteresis loop width in type-II superconductors,vanishes for samples smaller than a critical size. We argue that the SMP is not related to the critical current enhancement but can be well explained within a framework of the thermomagnetic flux-jump instability theory, where flux jumps reduce the absolute irreversible magnetization relative to the isothermal critical state value at low enough magnetic fields. The recovering of the isothermal critical state with increasing field leads to the SMP. The low-field SMP takes place in both Iow-Tc conventional and high-Tc unconventional superconductors. Our results show that the restoration of the isothermal critical state is responsible for the SMP occurrence in both cases.