Impact of cosmic rays on Population III star formation     

Athena Stacy  Volker Bromm 《Monthly notices of the Royal Astronomical Society》2007,382(1):229-238

We explore the implications of a possible cosmic-ray (CR) background generated during the first supernova explosions that end the brief lives of massive Population III stars. We show that such a CR background could have significantly influenced the cooling and collapse of primordial gas clouds in minihaloes around redshifts of   z ∼ 15–20  , provided the CR flux was sufficient to yield an ionization rate greater than about 10⁻¹⁹ s⁻¹ near the centre of the minihalo. The presence of CRs with energies  ≲10⁷  eV would indirectly enhance the molecular cooling in these regions, and we estimate that the resulting lower temperatures in these minihaloes would yield a characteristic stellar mass as low as  ∼10 M_⊙  . CRs have a less-pronounced effect on the cooling and collapse of primordial gas clouds inside more massive dark matter haloes with virial masses  ≳10⁸ M_⊙  at the later stages of cosmological structure formation around   z ∼ 10–15  . In these clouds, even without CR flux the molecular abundance is already sufficient to allow cooling to the floor set by the temperature of the cosmic microwave background.  相似文献   

Bacterial ancient DNA as an indicator of human presence in the past: its correlation with palynological and archaeological data     

Jacek Madeja  Agnieszka Wacnik  Agata Zyga  Elzbieta Stankiewicz  Ewa Wypasek  Witold Guminski  Krystyna Harmata 《第四纪科学杂志》2009,24(4):317-321

Palynological investigation is one of the most important tools for reconstructing past vegetation. Some plants have proved to be relatively sensitive indicators of human activity, but most of them are not specific. In this paper we propose a method which can be used for the verification of phases of anthropogenic impact on vegetation distinguished in pollen diagrams. In this work we adopted the existing molecular methods for tracking bacterial ancient DNA of Bifidobacterium and Bacteroides‐Prevotella (known as human‐ and cow‐specific genetic markers) in palynologically and archaeologically associated sediments. This method can be helpful in determining local human presence, especially in those time periods when pollen analysis has not always been very discriminating (Palaeolithic, Mesolithic) and at sites without archaeological evidence. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

The effect of management choices on the sustainability and economic performance of a mixed fishery: a simulation study     

Kraak  S. B. M.; Buisman  F. C.; Dickey-Collas  M.; Poos  J. J.; Pastoors  M. A.; Smit  J. G. P.; van Oostenbrugge  J. A. E.; Daan  N. 《ICES Journal of Marine Science》2008,65(4):697-712

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Astrophysical and cosmological information from large-scale submillimetre surveys of extragalactic sources     

M. Negrello  F. Perrotta  J. González-Nuevo González  L. Silva  G. De Zotti  G. L. Granato  C. Baccigalupi  L. Danese 《Monthly notices of the Royal Astronomical Society》2007,377(4):1557-1568

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星洲银罗非鱼线粒体细胞色素b基因的序列分析   总被引：1，自引：1，他引：0  

刘楚吾  李路  林晓坤  刘丽 《广东海洋大学学报》2008,28(4)

克隆并测定了星洲银罗非鱼(Oreochromis sp.)细胞色素b基因(cyt b)的全序列,得到全长1 141bp的序列用于分析,用MEGA4.0分析软件与GenBank中的线粒体DNA序列进行序列比较,显示星洲银罗非鱼与其他鱼类的cyt b基因的同源性较高,同源度介于83%~93%间;根据星洲银罗非鱼与莫桑比克罗非鱼、尼罗罗非鱼等12种鱼类的cyt b基因序列构建的系统进化树,初步确定尼罗罗非鱼、莫桑比克罗非鱼为星洲银罗非鱼的父母本。  相似文献   

Application of the Clustering Method in Molecular Dynamics Simulation of the Diffusion Coefficient     

LIU Qingzhi HU Yangdong 《中国海洋大学学报(英文版)》2008,7(1):43-47

Using molecular dynamics （MD） simulation, the diffusion of oxygen, methane, ammonia and carbon dioxide in water was simulated in the canonical NVT ensemble, and the diffusion coefficient was analyzed by the clustering method. By comparing to the conventional method （using the Einstein model） and the differentiation-interval variation method, we found that the results obtained by the clustering method used in this study are more close to the experimental values. This method proved to be more reasonable than the other two methods.  相似文献   

Improved HCN/HNC linelist, model atmospheres and synthetic spectra for WZ Cas     

G. J. Harris  J. Tennyson  B. M. Kaminsky  Ya. V. Pavlenko  H. R. A. Jones 《Monthly notices of the Royal Astronomical Society》2006,367(1):400-406

We build an accurate data base of 5200 HCN and HNC rotation–vibration energy levels, determined from existing laboratory data. 20 000 energy levels in the Harris et al. linelist are assigned approximate quantum numbers. These assignments, lab-determined energy levels and Harris et al. energy levels are incorporated in to a new energy level list. A new linelist is presented, in which frequencies are computed using the lab-determined energy levels where available, and the ab initio energy levels otherwise.
The new linelist is then used to compute new model atmospheres and synthetic spectra for the carbon star WZ Cas. This results in better fit to the spectrum of WZ Cas in which the absorption feature at 3.56 μm is reproduced to a higher degree of accuracy than has previously been possible. We improve the reproduction of HCN absorption features by reducing the abundance of Si to [Si/H]=−0.5 dex, however, the strengths of the Δ v = 2 CS band heads are overpredicted.  相似文献   

两种体色画眉笛雕的遗传多样性及分子标记     

刘丽  刘楚吾  岳文 《广东海洋大学学报》2008,28(3)

根据体侧纵带颜色差异,暂将画眉笛鲷(Lutjanus vitta)分为黄带画眉笛鲷和褐带画眉笛鲷,应用RAPD技术,选用22个引物对黄带画眉笛鲷与褐带画眉笛鲷进行遗传多样性及分子标记研究。结果表明,黄带画眉笛鲷与褐带画眉笛鲷的遗传距离为0.832 9,其多态位点比例(P)分别为66.99%和85.28%,遗传多样性指数(H)分别为0.161 7和0.289 3,种内遗传距离(D)分别为0.243 5和0.431 9,表明褐带画眉笛鲷的遗传多样性比黄带画眉笛鲷丰富。共得到OPP14-629bp和OPP14-674bp等11个特异性分子标记,可用于两种笛鲷的鉴定。  相似文献   

Effects of AlN nucleation layer thickness on crystal quality of AlN grown by plasma-assisted molecular beam epitaxy     

任凡  郝智彪  胡健楠  张辰  罗毅 《海洋学报(英文版)》2010,29(11)

In this paper, the effects of thickness of AlN nucleation layer grown at high temperature on AlN epi-layer crystalline quality are investigated. Crack-free AlN samples with various nucleation thicknesses are grown on sapphire substrates by plasma-assisted molecular beam epitaxy. The AlN crystalline quality is analysed by transmission electron microscope and x-ray diffraction (XRD) rocking curves in both (002) and (102) planes. The surface profiles of nucleation layer with different thicknesses after in-situ annealing are also analysed by atomic force microscope. A critical nucleation thickness for realising high quality AlN films is found. When the nucleation thickness is above a certain value, the (102) XRD full width at half maximum (FWHM) of AlN bulk increases with nucleation thickness increasing, whereas the (002) XRD FWHM shows an opposite trend. These phenomena can be attributed to the characteristics of nucleation islands and the evolution of crystal grains during AlN main layer growth.  相似文献   

强场和弱场侧超声分子束注入对加料的影响     

焦一鸣  姚良骅  冯北滨  陈程远  周艳  石中兵  董家齐  段旭如 《海洋学报》2010,32(10):7191-7197

报道了HL-2A装置最新的实验结果,讨论并研究了超声分子束的注入位置对分子束在等离子体中的消融和穿透的影响,其中包括电离后的分子束粒子在磁场梯度作用和 E × B 漂移下的加速或减速及由此形成的冷通道效应.研究结果表明,磁场梯度和 E × B 漂移对于超声分子束的加料效果、消融和穿透有着重要的作用.强场侧注入可使电离后的电子和离子更深地进入等离子体芯部.这些研究对于更好地理解超声分子束与等离子体的相互作用和优化设计加料系统有一定作用.  相似文献