Electron-impact rotational excitation of linear molecular ions

Molecular R -matrix calculations are performed to give rotational excitation rates for electron collisions with linear molecular ions. Results are presented for CO⁺, HCO⁺, NO⁺ and H₂⁺ up to electron temperatures of 10 000 K. De-excitation rates and critical electron densities are also given. It is shown that the widely used Coulomb–Born approximation is valid for Δ j =1 transitions when the molecular ion has a dipole greater than about 2D, but otherwise is not reliable for studying electron-impact rotational excitation. In particular, transitions with Δ j >1 are found to have appreciable rates and are found to be entirely dominated by short-range effects.     

Nearby Protoclusters as Laboratories for Understanding Star Formation on Galactic Scales

Detailed studies of nearby cluster-forming molecular clouds can help us understand the physical processes by which most stars form in galaxies. I review recent advances made on this subject. Submillimeter observations of nearby protoclusters suggest that stars are generally built from finite, detached reservoirs of mass inside molecular cloud cores, and point to a cloud fragmentation origin for the IMF. Much progress in this field will come from future large submillimeter instruments such as Herschel and ALMA. This revised version was published online in September 2006 with corrections to the Cover Date.     

稀有金属花岗岩富集成矿的烃类气体地球化学标志——以广西栗木锡多金属矿为例

烃类气体在自然界广泛分布并具有复杂成因和来源,同时针对烃类气体的研究不应局限于石油、天然气等传统能源矿产,而需要推广到更多其他科研领域。笔者等采取苦橄岩烃类气体标准化的研究思路,以广西栗木锡多金属矿为中心,重点围绕矿区各阶段花岗岩、矿体及地表土壤开展烃类气体宏观特征和微观规律的研究工作。通过研究和对比,揭示花岗岩及矿石中烃类气体特征和变化规律,查明在成矿作用影响下烃类气体成熟度提高且通过构造裂隙向上运移,并被地表土壤吸附形成异常的事实,明确了深部隐伏矿体与土壤烃类气体异常的成因联系及空间对应关系,建立了判断稀有金属花岗岩富集成矿的烃类气体特征指标和参数,研究表明,将烃类气体特征作为判断稀有金属花岗岩富集成矿地球化学标志的思路正确且方法可行,并将对今后进一步拓展烃类气体的研究和应用领域产生积极影响。     

水(冰):宇宙矿物

水(冰)是最简单的化合物,也是宇宙中丰度最大的矿物。通常认为,水无嗅、无味,无处不在。然而,液态水或固态水却是异乎寻常的物质。水具有某些其它物质没有的,特别是赋予生命所要求的特殊性质,如氢键、水簇和kosmotrope离子等。本文综述水(冰)的结构、化学性质、物理性质、分布以及与生命的关系。     

一种模拟韧性剪切带中椭球状标志体运动、变形的新方法

韧性剪切带中赋存的椭球状应变标志体(砾石、碎斑等)是研究剪切带运动学、动力学的重要应变标志体。传统研究中椭球状标志体通过对野外露头的观测或与实验岩石学结合,判断剪切带运动方向、探讨运动学和流变学特征。随着数值模拟技术在韧性剪切带中的引入和推广,国内外许多学者试图恢复椭球状标志体的运动轨迹和变形特征,并取得了显著的成果。然而,国内文献对于模拟韧性剪切带椭球状标志体的定量及模拟研究甚少,研究方法也鲜为介绍。基于此,针对韧性剪切带中椭球状标志体变形的最新研究进展,详细介绍建立在Jeffery理论和Eshelby理论之上的数值模拟思路和方法,并利用Mathcad软件模拟了给定条件下的椭球状标志体的运动轨迹、变形特征。     

A Study on the CO Isotopic Lines of the Star Forming Region AFGL 5157

By the mapping observations simultaneously at the ¹²CO (J=1-0), ¹³CO (J=1-0), and C¹⁸O (J=1-0) lines on the area of 24’×24’ (12 pc×12 pc) of the star forming region AFGL 5157, we have obtained the distribution and averaged physical parameters for the respective ¹³CO and C¹⁸O cores of this molecu- lar cloud. At the edge of the molecular cloud, the isotopic abundance ratio is X [(¹³CO)/(C¹⁸O)] ≈ 10, close to the ratio of a giant molecular cloud. The viral masses of the ¹³CO and C¹⁸O cores are less than the masses of the molecu-lar cloud cores, so the molecular cloud cores are gravitationally unstable, and the C¹⁸O molecular cloud core is more easy to collapse. The column density distributions of the C¹⁸O molecular cloud core in the northeast and southwest directions are, respectively, 1.1 × 10²³× z^−0.43 and 4.6 × 10²⁵× z^−0.58, where z is the distance from the center of the molecular cloud core. The high velocity molecular out?ow has been con?rmed from our ¹²CO spectra, the mass loss rate of the out?ow has been estimated, and the mass-velocity relation of the out?ow is ?tted by a power-law function of m ∝ v^−1.8. The star formation rate of the ¹³CO molecular cloud core is as high as 23%, probably, under the in?uence of     

Low velocity shock-cloud encounters I.

Shocks propagating in the interstellar medium (ISM) play an important role in the life of molecular clouds. Through a theoretical study of interaction between clouds and shocks we can understand, for example, the density distribution of observed molecular clouds and the first steps of star formation. The only way to study of interaction in detail is via a numerical hydrodynamical simulation. In this paper we present the first results of a hydrocode which is able to follow the processes after the collision between the cloud and shock front.Our main theoretical result is that the chemical processes (e.g. H₂ dissociation) can affect the dynamical processes significantly. Global parameters of the cloud are calculated for the comparision of the simulation and the observations.     

Dense Gas Diagnostics: Maser Excitation and Variability

I review a number of diagnostic techniques, based upon the excitation and variability of astrophysical masers, which can be applied to dense gas. In each case, I consider the observations necessary and the amount of interpretation, or modelling, required to complete the analysis of a source, presenting examples of each diagnostic method.