Impact angle influence in high velocity dust collisions during planetesimal formation

We have examined the influence of impact angle in collisions between small dust aggregates and larger dust targets through laboratory experiments. Targets consisted of μm-sized quartz dust and had a porosity of about 67%; the projectiles, between 1 and 5 mm in diameter, were slightly more compact (64% porosity). The collision velocity was centered at 20 m/s and impact angles range from 0° to 45°. At a given impact angle, the target gained mass for projectiles smaller than a threshold size, which decreases with increasing angle from about 3 mm to 1 mm. The fact that growth is possible up to the largest angles studied supports the idea of planetesimal formation by sweep-up of small dust aggregates.     

Relaxation of protostellar accretion shocks using the smoothed particle hydrodynamics

It is believed that protostellar accretion disks are formed from nearly ballistic infall of molecular matter in rotating core collapse. Collisions of this infalling matter leads to formation of strong supersonic shocks, which if they cool rapidly, result in accumulation of that material in a thin structure in the equatorial plane. Here, we investigate the relaxation time of the protostellar accretion post‐shock gas using the smoothed particle hydrodynamics (SPH). For this purpose, a one‐dimensional head‐on collision of two molecular sheets is considered, and the time evolution of the temperature and density of the post‐shock region simulated. The results show that in strong supersonic shocks, the temperature of the post‐shock gas quickly increases proportional to square of the Mach number, and then gradually decreases according to the cooling processes. Using a suitable cooling function shows that in appropriate time‐scale, the center of the collision, which is at the equatorial plane of the core, is converted to a thin dense molecular disk, together with atomic and ionized gases around it. This structure for accretion disks may justify the suitable conditions for grain growth and formation of proto‐planetary entities (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

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)     

X‐shooting Herbig Ae/Be stars: Accretion probed by near‐infrared He I emission

The Herbig Ae/Be stars are intermediate mass pre‐main sequence stars that bridge the gap between the low mass T Tauri stars and the Massive Young Stellar Objects. In this mass range, the acting star forming mechanism switches from magnetically controlled accretion to an as yet unknown mechanism, but which is likely to be direct disk accretion onto the star. We observed a large sample of Herbig Ae/Be stars with X‐shooter to address this issue from a multi‐wavelength perspective. It is the largest such study to date, not only because of the number of objects involved, but also because of the large wavelength coverage from the blue to the near‐infrared. This allows many accretion diagnostics to be studied simultaneously. By correlating the various properties with mass, temperature and age, we aim to determine where and whether the magnetically controlled mass accretion mechanism halts and the proposed direct disk accretion takes over. Here, we will give an overview of the background, present some observations and discuss our initial results. We will introduce a new accretion diagnostic for the research of Herbig Ae/Be stars, the HeI 1.083 μm line (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Tube-forming polychaetes enhance invertebrate diversity and abundance in sandy sediments of Mozambique,Africa

In marine soft-bottom systems, polychaetes can increase habitat complexity by constructing rigid tubes (e.g. several onuphid species) that contrast with surrounding topographically flat sediments. These structures can provide predation refuges and increase larval settlement and thereby increase the richness and abundance of fauna. We collected invertebrate samples from an intertidal flat with low onuphid tube density (2.7 m^–2) in Mozambique and document that more organisms (70 times higher mollusc abundances) and more species (15 times more mollusc species) were found associated with solitary tubes of an onuphid polychaete compared with surrounding sand habitats. These results are in agreement with tube versus sand comparisons from soft-bottom systems in the North Atlantic where polychaete tube densities are often much higher.     

渤海古近系东营组三角洲相油田地质特征研究

渤海古近系东营组三角洲相油田是渤海油田的主力含油层系.从构造、储层与沉积、流体和油藏等方面对渤海海域东营组三角洲相油田地质特征进行了研究,按河流三角洲和辫状河三角洲相砂岩油藏两种沉积相类型分别对储层分布特征进行了描述.在此基础上探讨了此类油田的流体分布特点和油藏模式,并认为渤海东营组三角洲相油田以中到大型为主,储层岩性大都属于高孔高渗的疏松砂岩,储层具有分布较稳定、油层厚和物性好等特点,原油以普通稠油为主,其次是中、低黏油.     

川东北飞仙关组沉积控储机理研究

在礁滩型碳酸盐岩储层中,沉积对储层发育的控制作用至关重要。以川东北普光和元坝地区的下三叠统飞仙关组台地边缘浅滩相储层为例,在沉积背景及其演化分析的基础上,研究了飞仙关组沉积亚相及微相发育特征,划分并描述了典型钻井储层高频旋回,讨论了层序演化对储层发育的控制作用,高频旋回发育及其与孔隙发育的相关性、相对海平面变化与储层非均质性的关系,以及沉积、成岩环境对储层早期孔隙发育的控制作用。     

水平井中随钻电阻率实时确定地层界面方法

实时确定地层界面是水平井地质导向钻井中的重要问题之一。考虑到泥浆电阻率、井眼在一定范围内对随钻电磁波影响较小,把三维地层模型简化为一维地层模型,大大减少了正演计算量。利用马奎特方法对其进行了实时反演计算,获得了仪器与地层界面之间的距离。实验表明,所确定的地层界面位置与实际相吻合,能够控制仪器的运行轨迹,使井眼保持在期望的地层内,有效提高了水平井的随钻地质导向能力。     

延长探区下古生界马家沟组储层流体包裹体特征

流体包裹体研究在划分油气运移充注期次、确定油气藏形成时间等方面均有重要的应用价值.通过镜下观察流体包裹体的特征,划分类型,描述其特征,对与烃类共生的盐水包裹体进行均一化温度测试,并结合其他相关地质资料,认为延长探区马家沟组储层流体包裹体的均一温度集中分布在85~115℃范围内,包裹体捕获时的埋藏深度为2500~2800 m.结合盆地的埋藏史推测天然气成藏时间为晚三叠-早侏罗世.     

吉林塔东铁矿赋矿建造地球化学特征及其地质构造意义

塔东铁矿严格受层位控制,产于新元古界塔东群拉拉沟岩组中,属于大型沉积变质型磁铁矿床.赋矿火山岩岩石化学成分具有低SiO₂、高MgO、富Na₂O的地球化学特征,火山岩成分点集中分布于造山带（岛弧或活动大陆边缘）火山岩区;亲幔元素（Cr、Ni、Co）相对亏损,大离子亲石元素相对富集;含有较高的总稀土和高度富集LREE,贫HREE,显示在火山岩成分中加入较多的陆壳成分.该矿床形成于与板块俯冲体系有关的岛弧或活动大陆边缘构造背景.