Studies of dust grain properties in infrared reflection nebulae

We have developed a model for reflection nebulae around luminous infrared sources embedded in dense dust clouds. The aim of this study is to determine the sizes of the scattering grains. In our analysis, we have adopted an MRN-like power-law size distribution (Mathis, Rumpl, and Nordsieck) of graphite and silicate grains, but other current dust models would give results which were substantially the same. In the optically thin limit, the intensity of the scattered light is proportional to the dust column density, while in the optically thick limit, it reflects the grain albedo. The results show that the shape of the infrared spectrum is the result of a combination of the scattering properties of the dust, the spectrum of the illuminating source, and foreground extinction, while geometry plays a minor role. Comparison of our model results with infrared observations of the reflection nebula surrounding OMC-2/IRS 1 shows that either a grain size distribution like that found in the diffuse interstellar medium, or one consisting of larger grains, can explain the observed shape of the spectrum. However, the absolute intensity level of the scattered light, as well as the observed polarization, requires large grains (approximately 5000 angstroms). By adding water ice mantles to the silicate and graphite cores, we have modeled the 3.08 micrometers ice band feature, which has been observed in the spectra of several infrared reflection nebulae. We show that this ice band arises naturally in optically thick reflection nebulae containing ice-coated grains. We show that the shape of the ice band is diagnostic of the presence of large grains, as previously suggested by Knacke and McCorkle. Comparison with observations of the BN/KL reflection nebula in the OMC-1 cloud shows that large ice grains (approximately 5000 angstroms) contribute substantially to the scattered light.     

富源刺托洞旧石器遗址初探

富源刺托洞的旧石器文化是适应岩溶地貌发育环境的产物,形成以小型石片、刮削器为主体的石器工业;当时的气候总体上是在热带、亚热带气候至暖温带之间波动,形成的动物群为非典型的大熊猫-剑齿象动物群(Ailuroooda-Stegodon fauna)可与晚更新世的柳江动物群(西畴动物群)对比;遗址时代为晚更新世,地质年龄测定(14C)＞4×104a.     

关于冰川学和冻土学外文核心期刊之确定

以英国出版的《极地与冰川文摘》为统计蓝本，据文摘法确定冰种学和冻土学的外文核心期刊，并按学科对这些期刊进行分类，指出《自然》、《科学》和《国际学位论文文摘：Ｂ》等自然科学综合性期刊在冰川学和冻土学核心期刊中的重要性以及冰川学和冻土学的发展趋势。     

《土的冻结作用与地基》评介

2007年1月陈肖柏等先生的新著《土的冻结作用与地基》已由科学出版社出版发行.作为一个普通读者拜读了之后,不由地说:“一本好书”.全书由基础篇和应用篇两部分组成.第一章至第十一章为土冻结作用的基础篇.第一章是开宗明义的一章.作者通过许多实例来概述国内外多年冻土和深季节冻土地区的工程冻害,从而指出在我国寒区经济迅猛发展的今天,认识工程冻害的机制,然后控制与预防之,有着极为重要的意义.第二章简要叙述了全球冻土(尤其是我国冻土)的分布、土的冻融过程热特征和基本方程.     

印度深水油气的勘探机遇与挑战

科学与技术的发展使海上油田钻探和生产技术在过去５０ａ发生了显著进步 ,导致１９４７年在墨西哥湾水深２０英尺处安装了第一个海上平台 ,随后深浅海区在确定、开发和利用新、老油田的方法上取得了巨大进展。随着技术的发展 ,深水定义也随时间发生了变化。２０世纪７０年代深水界限为１００ｍ ,到８０年代晚期则为３００ｍ。遥控器（ＲＯＶｓ）和电子遥控系统的发展将深水的范围扩展至现今的３０００ｍ。现已在世界数个深水地区发现了油气储量。过去８ａ在墨西哥湾水深５００～１８００ｍ圈定储量超过５０亿桶 ;在巴西的Ｃａｍｐｏｓ盆地 ,…     

Inter-annual variability of wet season freshwater plume extent into the Great Barrier Reef lagoon based on satellite coastal ocean colour observations

Riverine freshwater plumes are the major transport mechanism for nutrients, sediments and pollutants into the Great Barrier Reef (GBR) lagoon and connect the land with the receiving coastal and marine waters. Knowledge of the variability of the freshwater extent into the GBR lagoon is relevant for marine park management to develop strategies for improving ecosystem health and risk assessments. In this study, freshwater extent has been estimated for the entire GBR lagoon area from daily satellite observations of the Moderate Resolution Imaging Spectroradiometer (MODIS) between 2002 and 2010. To enable a reliable mapping of freshwater plumes we applied a physics-based coastal ocean colour algorithm, that simultaneously retrieves chlorophyll-a, non-algal particulate matter and coloured dissolved organic matter (CDOM), from which we used CDOM as a surrogate for salinity (S) for mapping the freshwater extent.