Desorption processes and the deuterium fractionation in molecular clouds

Several processes have been suggested as ways of returning accreted grain mantles to the gas, thus preventing the total removal of molecules from the gas phase in dark quiescent clouds. We attempt to distinguish between them by considering not only the calculated gas-phase abundances, but also the ratio of the abundances of deuterated species to non-deuterated species. We find that the D/H ratio in molecules is relatively model-independent, but that desorption due to the formation of H₂ on grains gives the best overall agreement with the observations.     

HE 1127–1304: the largest radio quasar

By considering the propagation of low-amplitude magnetohydrodynamic waves in partially ionized plasmas, it is shown that the ion-neutral drift (ambipolar diffusion) induced by the waves can have specific effects on the molecular chemistry of cold material. The chemistry occurring in gas swept by Alfvén waves is described and it is shown that this leads to spatial variations in the deuterium fractionation ratios of, for example, HCO⁺ and N₂H⁺, on spatial scales of a few hundredths of a parsec, depending upon the fractional ionization of the ambient medium. The possibility of detecting interstellar Alfvén waves by molecular spectroscopy and their effect of producing small-scale chemical abundance gradients in molecular clouds are briefly discussed.     

The binary star population of the young cluster NGC 1818 in the Large Magellanic Cloud

We determine the binary star fraction as a function of radius in NGC 1818, a young rich cluster in the Large Magellanic Cloud, using Hubble Space Telescope images in bands F336W (∼ U ) and F555W (∼ V ). Our sample includes binaries with M _primary ∼ 2–5.5 M_⊙ and M _secondary ≳ 0.7 M_primary. The binary fraction increases towards the cluster centre, from ∼ 20 ± 5 per cent in the outer parts, to ∼ 35 ± 5 per cent inside the core. This increase is consistent with dynamical mass segregation and need not be primordial. We compare our results with expectations from N -body models, and discuss the implications for the formation and early evolution of such clusters.     

论东川脉状富铜矿的历史和现实意义

东川脉状富铜矿在历史上对矿山、对国家曾作出过重大贡献。汤丹厚大的层状铜矿也是５０年代在广泛调查汤丹脉状矿的基础上发现的，从而肯定整个东川矿区层状矿的巨大工业价值。对脉状铜矿的成因，长期以来受着“脉状铜矿由层状铜矿就地取材”转化形成的思想束缚，因而对其评价－研究成果甚少。从脉矿现有的历史资料出发，结合当今的研究成果，认为东川矿区广泛分布含铜大于５％的富脉矿，脉矿与层状矿在伴生元素、稀土配分、硫同位素组成，爆裂测温等方面，二者均有明显的区别。脉铜矿是以深源为主形成的。建议对历史上曾开采，但至今未作详细地质工作的茂麓铜厂尽快予以评价。     

A STUDY OF MICROWAVE RADIATION TRANSFER CHARACTERISTICS IN STRATIFIED PRECIPITATION CLOUDS BY COMBINING STRATIFIED CLOUD MODEL WITH MICROWAVE RADIATION TRANSFER MODEL

In this paper,the effect of precipitation particles on microwave radiation transfer characteristics in stratified clouds over the ocean is studied by combining stratified cloud model with microwave radiation transfer model.By comparing the calculated results with the true data,it is found that precipitation particle distribution and water shell around ice phase particle strongly affect the upwelling radiation.Therefore,the precipitation particle distribution and water shellaround ice phase particle must be considered when a calculating scheme is designed for retrieving precipitation in stratified clouds by the use of microwave radiation transfer model.     

Magnetic clouds and interplanetary particle transport: a numerical model

Magnetic clouds modify the structure of the interplanetary magnetic field on spatial scales of tenth of AU. Their influence on the transport of energetic charged particles is studied with a numerical model that treats the magnetic cloud as an outward propagating modification of the focusing length. As a rule of thumb, the influence of the magnetic cloud on particle intensity and anisotropy profiles increases with decreasing particle mean free path and decreasing particle speed. Three cases are considered: (1) when the magnetic cloud is the driver of a shock that accelerates particles as it propagates outward, (2) when the magnetic cloud interacts with a prior solar energetic particle event, and (3) when a magnetic cloud already is present in interplanetary space at the time of a solar energetic particle event. In the latter case the cloud acts as a barrier, storing the bulk of the particles in its downstream medium.     

基于区域生长法激光扫描数据平面特征提取

激光扫描测量技术在三维城市建模领域的应用具有良好的发展发展前景。本文中的方法可以更好的应用于激光扫描仪点云数据中的关键地物提取。本文首先对三维激光扫描仪的测距原理进行了介绍,分析了三维激光扫描仪点云数据中的平面表示方式,结合区域生长算法对激光扫描仪点云数据进行分割,从而提取出平面特征,最后对该方法进行了试验和分析。     

复杂城市环境的机载Lidar点云滤波(英文)

A novel filtering algorithm for Lidar point clouds is presented, which can work well for complex cityscapes. Its main features are filtering based on raw Lidar point clouds without previous triangulation or rasterization. 3D topological relations among points are used to search edge points at the top of discontinuities, which are key information to recognize the bare earth points and building points. Experiment results show that the proposed algorithm can preserve discontinuous features in the bare earth and has no impact of size and shape of buildings.     

红外暗云中分子气体团块的性质研究

利用¹²CO(1-0)、¹³CO(1-0)与C¹⁸O(1-0)分子谱线成图观测数据,并结合ATLASGAL (The APEX(Atacama Pathfinder Experiment) Telescope Large Area Survey of the Galaxy)尘埃连续谱巡天观测结果详细地研究了9个红外暗云(Infrared Dark Clouds, IRDCs)中团块的物理性质与运动学特征.给出了红外暗云的速度区间,以及在红外暗云所对应的Spitzer (Spitzer Space Telescope) 8μm辐射背景上叠加了与红外暗云轮廓基本吻合的¹³CO和C¹⁸O积分强度分布图. 9个红外暗云中有8个呈纤维状结构.在这些红外暗云中共找出51个致密团块,质量偏大的团块大部分聚集在红外暗云的枢纽位置.质量统计直方图中表现出明显的双峰结构,进一步证实纤维状分子云物质输送的图景.¹²CO(1-0)计算所得的典型激发温度T_ex...