Large Cretaceous sphenodontian from Patagonia provides insight into lepidosaur evolution in Gondwana

Sphenodontian reptiles successfully radiated during Triassic and Jurassic times, but were driven almost to extinction during the Cretaceous period. The sparse Early Cretaceous record of sphenodontians has been interpreted as reflecting the decline of the group in favour of lizards, their suspected ecological successors. However, recent discoveries in Late Cretaceous beds in Patagonia partially modify this interpretation. Numerous skeletons of a new sphenodontian, Priosphenodon avelasi gen. et sp. nov., were collected from a single locality in the Cenomanian-Turonian Candeleros Formation, where it is more abundant than any other tetrapod group recorded in the quarry (for example, Crocodyliformes, Serpentes, Dinosauria and Mammalia). Adult specimens of Priosphenodon reached one metre in length, larger than any previously known terrestrial sphenodontian. Here we propose, using available evidence, that sphenodontians were not a minor component of the Cretaceous terrestrial ecosystems of South America, and that their ecological replacement by squamates was delayed until the early Tertiary. The new discovery helps to bridge the considerable gap in the fossil record (around 120 million years) that separates the Early Cretaceous sphenodontians from their living relatives (Sphenodon).     

Juxtaposed regions of extensive and minimal linkage disequilibrium in human Xq25 and Xq28

Linkage disequilibrium (LD), or the non-random association of alleles, is poorly understood in the human genome. Population genetic theory suggests that LD is determined by the age of the markers, population history, recombination rate, selection and genetic drift. Despite the uncertainties in determining the relative contributions of these factors, some groups have argued that LD is a simple function of distance between markers. Disease-gene mapping studies and a simulation study gave differing predictions on the degree of LD in isolated and general populations. In view of the discrepancies between theory and experimental observations, we constructed a high-density SNP map of the Xq25-Xq28 region and analysed the male genotypes and haplotypes across this region for LD in three populations. The populations included an outbred European sample (CEPH males) and isolated population samples from Finland and Sardinia. We found two extended regions of strong LD bracketed by regions with no evidence for LD in all three samples. Haplotype analysis showed a paucity of haplotypes in regions of strong LD. Our results suggest that, in this region of the X chromosome, LD is not a monotonic function of the distance between markers, but is more a property of the particular location in the human genome.     

岭南传统观演空间的视觉分析

通过对以神庙剧场为代表的岭南传统观演空间的视分析（包括城市空间的视觉分析和观演空间的视线分析），揭示岭南传统观演空间形态的规律和生存的双重意义，从而为研究岭南传统观演空间开辟一个理性的分析方法，并对现代剧场和城市公共空间的设计提供参考．     

商务英语的语言特点及教学策略

商务英语传达商务理论和实务等信息,在国际贸易活动中起着越来越重要的作用。文章通过分析商务英语语言词汇和表达方面的特点,结合自己的工作经验,提出相应的教学策略。     

图灵测试——机器是否有智能

<正>图灵测试的提出英国科学家图灵(Alan Turing)曾首先提出现代计算机的数学模型——图灵机。这个模型对后世计算机和计算机科学的发展有深远的影响。图灵因此而获得了极大的荣誉。目前世界上计算机科学的最高奖就是图灵奖。     

Research on 3D Micro-nano Processing Reported on Nature

The latest issue of Nature reported in its Research Highlights ( see " Lithography: Luminous Lizards", Nature, Vol. 451, p868, Feb. 21, 2008) that a group of researchers from the Technical Institute of Physics and Chemistry (TIPC), Chinese Academy of Sciences (CAS) achieved the new progress in 3D microstructures of nanometer composites using the multiphoton nanoprocessing technology.     

基于曲波变换的地震数据压缩感知重构算法

为提高地震数据压缩感知重构的信噪比和保真度, 提出一种基于曲波变换的地震数据压缩感知重构算法。建立了地震数据压缩感知重构模型, 分析了基于曲波变换稀疏表示的地震数据各尺度之间能量与熵的分布特性, 结合分块压缩感知技术降低随机观测的计算复杂度, 利用曲波变换稀疏表示高频区域各尺度之间的相关性, 设计了随信息熵变化的自适应双变量收缩阈值迭代重构的方法。实验结果表明, 在相同的采样率下,该算法重构的地震数据峰值信噪比提高了1. 5 dB 以上, 并且具有良好的细节信息保持能力。     

大型地下洞室群变形实测与数值模拟

以某水电站大型地下洞室群开挖为例,建立了三维数值分析模型,研究了洞室群开挖后洞周围岩的变形特性并分析了锚索应力损失对周围岩体变形和应力状态的影响;通过模拟结果与实测结果进行对比,分析模拟方法的合理性和支护方案的可行性.结果表明,围岩水平位移在洞室边墙中部最大,竖向位移在洞室拱顶最大,在洞室交叉部变形也较为显著;模拟结果与实测结果较接近,能良好地反映洞室实际开挖的过程和围岩的变形规律;锚索预应力损失达到某一程度时会使围岩水平位移显著增大.