Malthus foiled again and again

Throughout history, increasing population has driven the need to increase agricultural efficiency, so averting successive 'malthusian' disasters. In the twentieth century, the application of scientific knowledge to agriculture yielded tremendous dividends, enabling cereal yields to increase threefold since 1950. But with the world's population projected to reach nine billion by the middle of this century, new ways must be found to increase yields while preserving natural habitats and biodiversity.     

Out of Africa again and again

The publication of a haplotype tree of human mitochondrial DNA variation in 1987 provoked a controversy about the details of recent human evolution that continues to this day. Now many haplotype trees are available, and new analytical techniques exist for testing hypotheses about recent evolutionary history using haplotype trees. Here I present formal statistical analysis of human haplotype trees for mitochondrial DNA, Y-chromosomal DNA, two X-linked regions and six autosomal regions. A coherent picture of recent human evolution emerges with two major themes. First is the dominant role that Africa has played in shaping the modern human gene pool through at least two--not one--major expansions after the original range extension of Homo erectus out of Africa. Second is the ubiquity of genetic interchange between human populations, both in terms of recurrent gene flow constrained by geographical distance and of major population expansion events resulting in interbreeding, not replacement.     

月表线性构造与月海分布的动力学解释

目前,对月表的线性构造研究得很少,对月表月海、月陆分布的起因同样不明.“嫦娥一号”遥感探测表明:月表大部分线性构造集中分布于月球面向地球的正面(48°W-54°N),统计的86条月表线性其走向主要是N-S、NE-SW、NW-SE;22个月海大部分位于月球正面,且其中的20个月海分布在中低纬度(33.7°S-32.8°N).基于我们之前对地球板块动力学的认识,对月表的线性构造及月海分布的动力学解释是:引潮力引起了月表南北向的挤压和东西向的拉张,产生了N-S方向的挤压性破裂和在NW-SE,NE-SW方向产生的剪切性质的破裂,且月球正面所受的引潮力比背面大,所以线性构造多位于月球正面.通过引潮位φ=Gm/r0nΣn=2(a/r0)nPn(cosθ)的分析,月球在公转过程中,中低纬度受到的引潮位更大,在引潮力-重力共同作用下,形成的月球正面不仅壳薄而且裂隙多,岩浆向月壳薄弱的地方喷涌,形成分布在月球正面中低纬度的月海.     

月球探测的进展与我国月球探测的科学目标

在简述月球探测的历程与趋势的基础上,强调当代月球探测的总体目标为：(1)研究月球与地月系的起源和演化,特别是月球大气层与磁场的消失,矿物与岩石的分布和形成环境、月壤和内部层圈结构的形成以及月球演化的历程;(2)探测月球的资源、能源和特殊环境的开发利用及对人类社会长期可持续发展的支撑。我国不载人月球探测划分为绕、落及回三个阶段。为了全球性、整体性重新认识月球,绕月卫星探测的科学目标为获取全月面三维影像,探测14种有用元素的全球分布与丰度,探测月壤厚度并估算^3He资源量以及太阳活动对空间环境的影响。“落”为月球探测器软着陆就位探测和月球车巡视探测,建立月基光学、低频射电和极紫外天文观测平台。“回”为月球探测器软着陆就位探测和取样返回地面。     

罗睺与交食算法设计

罗睺与交食是藏传时轮历的核心部分,它预报日月食的食限数值、交食发生的时刻、食延时间、食分大小、入食方向等等。本文给出日月食预报的计算步骤以及一些重要数据的算法设计。