Convergent dental adaptations in pseudo-tribosphenic and tribosphenic mammals

Tribosphenic molars of basal marsupials and placentals are a major adaptation, with the protocone (pestle) of the upper molar crushing and grinding in the talonid basin (mortar) on the lower molar. The extinct pseudo-tribosphenic mammals have a reversed tribosphenic molar in which a pseudo-talonid is anterior to the trigonid, to receive the pseudo-protocone of the upper molar. The pseudo-protocone is analogous to the protocone, but the anteriorly placed pseudo-talonid is opposite to the posterior talonid basin of true tribosphenic mammals. Here we describe a mammal of the Middle Jurassic period with highly derived pseudo-tribosphenic molars but predominantly primitive mandibular and skeletal features, and place it in a basal position in mammal phylogeny. Its shoulder girdle and limbs show fossorial features similar to those of mammaliaforms and monotremes, but different compared with those of the earliest-known Laurasian tribosphenic (boreosphenid) mammals. The find reveals a much greater range of dental evolution in Mesozoic mammals than in their extant descendants, and strengthens the hypothesis of homoplasy of 'tribosphenic-like' molars among mammals.     

A second generation human haplotype map of over 3.1 million SNPs

We describe the Phase II HapMap, which characterizes over 3.1 million human single nucleotide polymorphisms (SNPs) genotyped in 270 individuals from four geographically diverse populations and includes 25-35% of common SNP variation in the populations surveyed. The map is estimated to capture untyped common variation with an average maximum r2 of between 0.9 and 0.96 depending on population. We demonstrate that the current generation of commercial genome-wide genotyping products captures common Phase II SNPs with an average maximum r2 of up to 0.8 in African and up to 0.95 in non-African populations, and that potential gains in power in association studies can be obtained through imputation. These data also reveal novel aspects of the structure of linkage disequilibrium. We show that 10-30% of pairs of individuals within a population share at least one region of extended genetic identity arising from recent ancestry and that up to 1% of all common variants are untaggable, primarily because they lie within recombination hotspots. We show that recombination rates vary systematically around genes and between genes of different function. Finally, we demonstrate increased differentiation at non-synonymous, compared to synonymous, SNPs, resulting from systematic differences in the strength or efficacy of natural selection between populations.     

Genome-wide detection and characterization of positive selection in human populations

With the advent of dense maps of human genetic variation, it is now possible to detect positive natural selection across the human genome. Here we report an analysis of over 3 million polymorphisms from the International HapMap Project Phase 2 (HapMap2). We used 'long-range haplotype' methods, which were developed to identify alleles segregating in a population that have undergone recent selection, and we also developed new methods that are based on cross-population comparisons to discover alleles that have swept to near-fixation within a population. The analysis reveals more than 300 strong candidate regions. Focusing on the strongest 22 regions, we develop a heuristic for scrutinizing these regions to identify candidate targets of selection. In a complementary analysis, we identify 26 non-synonymous, coding, single nucleotide polymorphisms showing regional evidence of positive selection. Examination of these candidates highlights three cases in which two genes in a common biological process have apparently undergone positive selection in the same population:LARGE and DMD, both related to infection by the Lassa virus, in West Africa;SLC24A5 and SLC45A2, both involved in skin pigmentation, in Europe; and EDAR and EDA2R, both involved in development of hair follicles, in Asia.     

The medaka draft genome and insights into vertebrate genome evolution

Teleosts comprise more than half of all vertebrate species and have adapted to a variety of marine and freshwater habitats. Their genome evolution and diversification are important subjects for the understanding of vertebrate evolution. Although draft genome sequences of two pufferfishes have been published, analysis of more fish genomes is desirable. Here we report a high-quality draft genome sequence of a small egg-laying freshwater teleost, medaka (Oryzias latipes). Medaka is native to East Asia and an excellent model system for a wide range of biology, including ecotoxicology, carcinogenesis, sex determination and developmental genetics. In the assembled medaka genome (700 megabases), which is less than half of the zebrafish genome, we predicted 20,141 genes, including approximately 2,900 new genes, using 5'-end serial analysis of gene expression tag information. We found single nucleotide polymorphisms (SNPs) at an average rate of 3.42% between the two inbred strains derived from two regional populations; this is the highest SNP rate seen in any vertebrate species. Analyses based on the dense SNP information show a strict genetic separation of 4 million years (Myr) between the two populations, and suggest that differential selective pressures acted on specific gene categories. Four-way comparisons with the human, pufferfish (Tetraodon), zebrafish and medaka genomes revealed that eight major interchromosomal rearrangements took place in a remarkably short period of approximately 50 Myr after the whole-genome duplication event in the teleost ancestor and afterwards, intriguingly, the medaka genome preserved its ancestral karyotype for more than 300 Myr.     

微束X射线荧光分析谱仪及其对松针中元素的分布分析

介绍了一种小型的微束X射线荧光分析谱仪,它是由导管X光透镜和能量色散X射线荧光分析谱仪组成.谱仪具有较高的空间分辨率和能量分辨率.使用本谱仪对松树针叶进行了微区分析,得出各种元素沿松针长度方向和横切面径向的分布规律.结果表明使用X光透镜的微束X射线荧光分析方法可以实现植物样品的微区分析,有助于进一步了解植物的生长与元素迁移的关系.     

大型二维装箱问题及其禁忌算法研究

对大型二维装箱问题进行描述,提出求解该问题的禁忌算法.算法基于自然数编码,设计了货物的摆放规则和序列生成方式,采用二种邻域,根据邻域的不同,构造了两种禁忌表.算法采用惩罚函‘数处理空间利用率约束.介绍算法的原理,给出了具有代表性算例试验结果并且进行了分析.试验结果表明了提出的禁忌算法对优化大型二维装箱问题的有效性.     

水溶液中相转化制备六方相三氧化钼及其电化学嵌锂性质

三氧化钼(MoO3)以三种常见的物相存在:正交相、六方相和单斜相,前者为热力学稳定相,后两者为热力学介稳相.相对于稳定的正交相MoO3,介稳的六方相MoO3较难制备.笔者采用对已商品化的正交相MoO3再次结晶的方法制得了纯六方相MoO3.通过透射电镜(TEM)观察可知产物为均匀的纳米棒.实验结果表明合成的六方相MoO3的首次放电容量比商品化的正交相MoO3高.六方相MoO3有望成为理想的锂离子电池阴极材料.     

拐角式回转热管管内蒸汽温度分布

磁流变软启动传动装置引入拐角式回转热管作为散热工具.拐角式回转热管利用热管旋转时产生的离心力回液,结构简单,散热能力强.文中介绍了拐角式回转热管的结构及散热原理,以动量定理和Clausius-Clapeyron方程为手段,建立了拐角式回转热管管内蒸汽温度分布模型,为该类回转热管的可靠设计和工作性能分析提供了理论依据.     

基于多Agent可重构生产系统控制模型

为了提高和改善当前生产系统对多变市场竞争环境的响应特性和应变能力,借鉴人体的组织结构和运行机理,把制造资源视为被控对象,将生产系统分成控制器与被控对象两部分,建立生物型可重构生产系统控制模型,设计具有人体神经-内分泌-免疫系统控制性能及特点的控制器功能结构,并结合多Agent技术阐述生产系统自组织重构过程及其构件化信息处理技术. 结果表明,通过各Agent之间的协作,可形成一个协同、自治并支持全局优化的可重构生产系统.     

祁门县非物质文化遗产旅游资源开发研究

在阐述了非物质文化遗产与旅游发展关系的基础上,分析评价了祁门县非物质文化遗产旅游资源类型及开发现状,构筑了该县非物质文化遗产旅游产品体系,并针对目前开发过程中的困境提出了相应的开发、保障措施.