星系中心大质量黑洞及潮汐瓦解恒星事件

黑洞潮汐瓦解恒星事件(Tidal Disruption Events,TDE)是星系中心黑洞瓦解进入其潮汐瓦解半径内的恒星并吸积恒星碎片物质而产生的一种剧烈辐射耀发现象.TDE的能谱和光变特征中蕴含了中心黑洞和被瓦解的恒星的信息,为我们证实和普查宁静星系中的黑洞,研究其参数、吸积过程和喷流产生、以及核区星际介质等提供了可能.TDE还可能提供中等质量黑洞和双黑洞存在的证据.TDE的观测和理论已成为一个新开辟的天体物理研究领域,但目前的进展受制于探测到事件太少(尤其是在X射线波段),且观测数据普遍质量不高.TDE的发生率很低,要探测大样本的事例需要监测足够大的空间体积.爱因斯坦探针卫星(Einstein Probe,EP)覆盖了0.5–4 keV的软X射线波段(接近TDE耀发时的辐射峰值能段),具有大视场以及高灵敏度,非常利于对TDE的探测.预期爱因斯坦探针卫星每年可以发现约几十至上百例TDE,其中有约10例或更多具有相对论性喷流特征.这将使我们可以获得较为完备、具有统计意义的TDE的样本,为进一步研究黑洞的存在和统计性质、增长和演化、发现中等质量黑洞和大质量双黑洞等提供了新的途径.中国科学院空间科学战略性先导科技专项(编号:XDA15052100);;北京大学“985工程”建设项目“星团环境对双黑洞形成演化过程的干扰及其对引力波探测的影响”资

Anomalous Thermal Stability of Nd-Fe-Co-Al Bulk Metallic Glass

The thermal stability of Nd60Fe20Co10Al10 bulk metallic glass (BMG) has been studied by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), isochronal dilatation and compression tests. The results show that the glass transition of the BMG takes place quite gradually between about 460 and 650 K at a heating rate of 0.17 K/s. Several transformation processes are observed during continuous heating with the first crystallization process beginning at about 460 K, while massive crystallization takes place near the solidus temperature of the alloy. The positive heat of mixing between the two major constituents, Nd and Fe, and, consequently, a highly inhomogeneous composition of the attained amorphous phase are responsible for the anomalous thermal stability in this system. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved

Processes and Model of Rainfall-Infiltration on Slope Land Treated with PAM

作为一种新型高效的土壤结构改良剂 PAM,在一定条件下能显著地提高土壤入渗能力 ,减小坡面径流。采用室内人工模拟降雨试验 ,研究了不同 PAM覆盖度下降雨产流随时间的动态变化及其与雨强、坡度的关系 ,以及入渗率随时间的变化规律 ,分析了 PAM、坡度、雨强对入渗率的影响。结果表明 ,地表施加 PAM后土壤的入渗率及稳定入渗率都比未施 PAM显著提高。通过对比施加 PAM后 Kostiakov入渗模型与 Horton入渗模型的显著性 ,表明 Horton入渗公式的适用性更

Effects of polyacrylamide on soil hydrodynamic parameters

该文研究土壤结构改良剂对土壤水分动力学参数的影响。通过对试验数据进行初步分析后得出 :加入土壤结构改良剂后 ,土壤饱和导水率有所提高 ;各处理的非饱和扩散率与对照相比 ,施加土壤结构改良剂的处理 ,在水平土柱试验中 ,远水端同一距离处土壤含水率要低于对照处理的含水率 ;土壤结构改良剂具有良好的吸水和保水性能 ,使得土壤的持水能力增强。在水势相同的情况下 ,与对照相比 ,施加土壤结构改良剂的土壤可保持更多的水分 ,并增加土壤中有效水含量。施加部位不同 ,土壤结构改良剂对土壤所持水分的含量也有较大差别 ,说明在实际应用中土壤结构改良剂的施用方法和施用深度也是影响土壤水分状况的一个较为重要的因素

Laboratory Simulated Experiments on Control Over Furrow-Irrigation Induced Soil Erosion

灌溉地土壤侵蚀问题已经越来越引起人们的普通关注。该文采用微型水槽的室内模拟试验 ,对利用 PAM及波涌灌溉等技术减少沟灌引起的土壤侵蚀效果进行了试验研究 ,分析了在不同坡度、不同流量条件下 PAM及灌溉间歇时间对侵蚀的影响。结果表明 :PAM可显著减少沟灌土壤侵蚀量 ,地面坡度是地面灌溉土壤侵蚀最主要影响因素 ,而流量及波涌灌间歇时间对它的影响较小灌溉地土壤侵蚀问题已经越来越引起人们的普通关注。该文采用微型水槽的室内模拟试验 ,对利用 PAM及波涌灌溉等技术减少沟灌引起的土壤侵蚀效果进行了试验研究 ,分析了在不同坡度、不同流量条件下 PAM及灌溉间歇时间对侵蚀的影响。结果表明 :PAM可显著减少沟灌土壤侵蚀量 ,地面坡度是地面灌溉土壤侵蚀最主要影响因素 ,而流量及波涌灌间歇时间对它的影响较

Effect of facility management regimes on soil bacterial diversity and community structure

Organic agriculture is a sustainable alternative to conventional agriculture. However, little is known about the effect of both organic and conventional agriculture on the environment and on the soil microbial community. The hypothesis was that bacterial community structure is defined by different agronomic practices. The objective of this study was to show how cropping systems, organic and conventional facility management regimes affect bacterial community structure and diversity. The study was also intended to increase knowledge on the prediction of soil sustainability under specific agronomic practices. The Illumina platform Hiseq 2500 high-throughput sequencing technique was used to sequence facility soil bacteria 16S rRNA from 6 treatments (OS: organic management of Solanaceous vegetable continuous cropping; OL: organic management of leafy vegetable continuous cropping; OSL: organic management of leafy-Solanaceous vegetables rotation; CS: conventional management of Solanaceous vegetable continuous cropping; CL: conventional management of leafy vegetable continuous cropping; and CSL: conventional management leafy-Solanaceous vegetables rotation) in Shunyi District of Beijing in June 2016. A total of 17 278 operational taxonomic units (OTUs) and 318 851 effective sequences were detected in the sequence control condition. Compared with soil bacterial community composition, diversity, relative abundance and interaction between soil factors and bacteria in different treatments, the results showed great differences between organic and conventional soil samples in bacterial community composition, and with a higher diversity in organic management. Obvious differences were observed between crop rotation and continuous cropping for bacterial community composition under organic management, while there was no significant difference between crop rotation and continuous cropping for bacterial community composition under conventional management. Soil bacterial diversity for rotation treatments was higher under organic management. It was found that there were mainly 14 genera of bacterial community, including Sphingomonas (5.05%) and Bacillus (4.84%). The abundance of the 14 genera changed significantly between organic and conventional management. There were insecticides degrading bacteria (Sphingomonas, Pseudomonas and Agromyces), disease controlling bacteria (Blastococcus and Lysobacter) and nitrification promoting bacteria (Candidatus Entotheonella and Microvirga) in conventional system. There were plant growth promoting bacteria (Bacillus) and organism degrading bacteria (Arthrobacter, Bhargavaea, Bryobacter, Candidatus Solibacter, Acidothermus and Tumebacillus) in organic system. Redundancy analysis also showed that soil bacterial community was affected mainly by soil total phosphorus, available phosphorus, and soil organic matter. Organic matter-decomposing bacteria Tumebacillus, Candidatus Solibacter and Acidothermus were positive associated with soil organic matter content. Therefore, the difference between organic and conventional soil samples for bacterial community originated from different fertilizer use methods, insecticide use methods and management patterns. Crop rotation promoted soil nutrient cycle and disease control under organic management. The results suggested that ecological adaptation mechanisms of different functional micro-organisms had significant differences in facility vegetable soils under different facility management regimes. The study provided the basis for further studies on exploring and explaining the characteristics and adaptation mechanisms of micro-organisms in facility soils under different facility management regimes

高电荷态金属离子的产生实验研究

　为满足兰州重离子加速器的实验要求,在14.5GHz高电荷态ECR离子源上做了一系列产生金属离子的实验,尝试了多种方法,包括炉子加热及MIVOC(MetallicIonformVolatileCompounds)两种方法,其中,用炉子做的结果较理想。实验主要研究了铜、锌、镍多种电荷态离子的产生,具有代表性的是39euA的Cu13+,30euA的Zn15+和29euA的Ni10+。分别给出了这三种金属离子产生的多电荷态束流峰谱图,以及实验的一些其它现象及结果,并对其进行了讨论与总结