Hydrodynamic simulations of merging clusters of galaxies

We present the results of high-resolution AP³M+SPH simulations of merging clusters of galaxies. We find that the compression and shocking of the core gas during a merger can lead to large increases in bolometric X-ray luminosities and emission-weighted temperatures of clusters. Cooling flows are completely disrupted during equal-mass mergers, with the mass deposition rate dropping to zero as the cores of the clusters collide. The large increase in the cooling time of the core gas strongly suggests that cooling flows will not recover from such a merger within a Hubble time. Mergers with subclumps having one eighth of the mass of the main cluster are also found to disrupt a cooling flow if the merger is head-on. However, in this case the entropy injected into the core gas is rapidly radiated away and the cooling flow restarts within a few Gyr of the merger. Mergers in which the subcluster has an impact parameter of 500 kpc do not disrupt the cooling flow, although the mass deposition rate is reduced by ∼30 per cent. Finally, we find that equal mass, off-centre mergers can effectively mix gas in the cores of clusters, while head on mergers lead to very little mixing. Gas stripped from the outer layers of subclumps results in parts of the outer layers of the main cluster being well mixed, although they have little effect on the gas in the core of the cluster. None of the mergers examined here resulted in the intracluster medium being well mixed globally.     

Researches in China on the Effects of Tides on the Earth Rotation

In this paper the tidal phenomena on the Earth are concisely specified, including solid tides, ocean tides and atmospheric tides due to the luni-solar tide-generating force, and the Earth pole tide due to the motion of the Earth's rotation axis (polar motion); as well as their effects on the Earth rotation. The outcomes of scientific researches of Chinese astronomers on these topics are described in some detail. These researches deal with the mechanisms responsible for tidal effects on the earth rotation, and on the measurements of the Earth rotation parameters. Finally, the effects discovered by Chinese researchers on the measurements of the period and change in period of pulsars are discussed. These effects are very small in magnitude but not negligible.     

Methodical approach to distribution of epilithic and drifting algae communities in a French subalpine river: Inferences on water quality assessment

In a sub-alpine river, the Asse, with an unpredictable discharge regime, chlorophyll, density and taxonomic diversity of both drifting and periphytic communities were studied from a methodical approach. The investigations based on stamping two close cross-sections to know their spatial distributions in a heterogeneous bed substrate showed a heterogeneous pattern of colonization mainly influenced by hydrological variables as the current velocity, the size of the substrata (gravel-pebble-boulder). For the drifting algae, mainly composed with benthic species temporarily unhooked to the substrata, the heterogeneity of the distribution was reduced in fast flow which induced a mixing of the whole mass of water. For the periphyton, some results indicated that the greatest diversity and the highest chlorophyll concentration were found on pebble substratum where the current velocity was moderate. These results have also shown that the classical methods used to day for investigations were inadequate for most Mediterranean rivers. It was really difficult to estimate the water quality from classical index created for use in regular large plain rivers.     

地下水流面三维实体模型制作系统（V1．00）

简要介绍了地下水流面在维实体模型制作系统－GWT3D（V1．00）的实体建模技术及光线跟踪原理，对其绘图所需数据文件结构进行了必要说明，同时阐述了GWT3D的功能与特色，并给出了该软件在这地区绘制地下水流场三维实体模型的一个实用实例。GWT3D是由VisualC 6.O开发的Win32应用程序，采用Outloow98流行的动画工具条风格，能利用通和地下水流模拟软件（如Modfolw等）所提供的网格剖分及水位数据，给制近似逼真的三维地下水流形态，具有动画显示功能和TIF、BMP、GIF3种图像文件存储格式，是一个专业性和实用性较强的计算机图像制作软件。     

Fossil Rotifers and the Early Colonization of an Antarctic Lake

Early Holocene sediments from a continental Antarctic lake (Ace Lake, Vestfold Hills, East Antarctica) contained abundant fossil rotifers of the genus Notholca. The fossil is similar to specimens of Notholca sp. present in modern-day Ace Lake and other fresh and brackish lakes of the Vestfold Hills. Cyanobacteria and protists (chrysophyte cysts, dinoflagellate cysts, and rhizopod tests) were also recovered from the core samples. These sediments were deposited early in the freshwater phase of Ace Lake, soon after deglaciation of the area. The occurrence of this trophically diverse assemblage of organisms at an early stage in the evolution of the lake suggests either that they were part of an endemic Antarctic flora and fauna which pre-dated the last glacial maximum and survived in glacial refugia or that efficient intercontinental dispersal had occurred.     

东天山北部古生代重大构造事件及其对中亚造山带演化的启示：基于1∶5万板房沟幅和小柳沟幅地质调查新证据

本文基于新疆哈密地区1∶5万板房沟幅和小柳沟幅区域地质调查新成果,对东天山北部古生代的重大构造事件以及演化历史进行了系统的梳理。基于下志留统与奥陶系之间角度不整合、下石炭统与泥盆系之间平行不整合以及上石炭统二道沟组与下伏岩系之间的角度不整合的确定,揭示奥陶纪与志留纪之交、泥盆纪与石炭纪之交以及晚石炭世期间存在几次重大构造事件。结合古生代不同时期沉积大地构造背景转换、岩浆活动构造环境转换以及构造变形格式转换的地质新纪录,提出奥陶纪与志留纪之交的造山事件为北部阿尔曼太洋闭合导致准噶尔—吐哈地块与阿尔泰地块碰撞的响应;泥盆纪与早石炭世之间的造陆构造事件可能是北部卡拉麦里洋盆初始汇拢碰撞的响应,其平行不整合以及下伏的志留纪—泥盆纪较稳定环境的沉积序列预示着介于卡拉麦里洋盆与南部北天山洋盆之间的准噶尔—吐哈地块为古亚洲洋盆体系中相对刚性的稳定陆块区,研究区作为准噶尔—吐哈地块的北部被动陆缘受卡拉麦里洋盆汇聚的影响较小;晚石炭世的造山事件则表现为响应卡拉麦里洋盆闭合后周缘前陆盆地的演化,是早石炭世沿卡拉麦里缝合带发生陆块碰撞以来挤压构造作用峰期的产物,其奠定了东天山北部北西-南东向构造基本格局。本文还重新界定莫钦乌拉断裂为北天山构造带(准噶尔—吐哈地块)与东准噶尔构造带的构造-地层分区界线,推断其为卡拉麦里缝合带向南东的延伸,并讨论了早石炭世受控不同构造体制的沉积和岩浆纪录的空间差异性,认为早石炭世北部莫钦乌拉山区域为与北侧卡拉麦里洋盆闭合后周缘挤压前陆盆地的发育过程,而南部博格达—哈尔里克山则总体呈现为响应南侧北天山洋盆闭合后的碰撞后伸展裂谷发育过程。     

基于深度学习的太阳F_10.7辐射通量的短期预报研究

F_10.7太阳辐射通量作为输入参数被广泛运用于大气经验模型、电离层模型等空间环境模型,其预报精度直接影响航天器轨道预报精度.采用时间序列法统计了太阳辐射通量F10.7指数和太阳黑子数(SSN)的关系,给出了两者之间的线性关系,在此基础上提出了一种基于长短时记忆神经网络(Long and Short Term Memory,LSTM)的预报方法,方法结合了54 d太阳辐射通量指数和SSN历史数据来对F_10.7进行未来7 d短期预报,并与其他预报方法的预报结果进行了比较,结果表明:(1)所建短期预报7 d方法模型的性能优于美国空间天气预报中心(Space Weather Prediction Center, SWPC)的方法,预测值和观测值的相关系数(CC)达到0.96,同时其均方根误差约为11.62个太阳辐射通量单位(sfu),预报结果的均方根误差(RMSE)低于SWPC,下降约11%;(2)对预测的23、24周太阳活动年结果统计表明,太阳活动高年的第7 d F10.7指数预报平均绝对百分比误差(MAPE)最优可达12.9%以内,低年最优可达2...     

Studying the formation of massive stars with VLT/X‐shooter

The birth process and (early) evolution of massive stars is still poorly understood. Massive stars are rare, their birthplaces are hidden from view and their formation timescale is short. So far, our physical knowledge of these young massive stars has been derived from near‐IR imaging and spectroscopy, revealing populations of young OB‐type stars, some still surrounded by a (remnant?) accretion disk, others apparently “normal” main sequence stars powering H II regions. The most important spectral features of OB‐type stars are, however, located in the UV and optical range. With VLT/X‐shooter it is possible to extend the spectral coverage of these young massive stars into the optical range, to better determine their photospheric properties, to study the onset of the stellar wind, and to characterize the physical structure of the circumstellar disk (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)