单细胞真核生物的miRNA系统及其进化意义

miRNA系统在高等多细胞真核生物中得到了广泛深入的研究。近年来,人们在单细胞真核生物上的miRNA研究也取得了重要进展。这不仅丰富了人们对miRNA在整个生物界中的认识,更重要的是对于揭示miRNA这一表达调节系统是如何在生物界中起源进化的问题具有重要意义。该文结合作者在最低等单细胞真核生物——贾第虫上的研究结果,对该领域的研究进展作一概述,并对有关miRNA这一系统的起源进化问题进行了探讨。

宁夏新建二代林网主要害虫种群数量变动规律初探

本文在连续 3年 (1 993～ 1 995年 )大量调查的基础上 ,研究了宁夏新建二代林网主要造林树种的主要害虫种群数量消长动态和发生规律。结果表明 :新建林网中具有潜在危险性的主要害虫为 :光肩星天牛 (Anoplophora glabripennis Motsch.)、木蠹蛾 (Cossuscossus orientalis Gaede &H olcocerus vicarius(Walker) )、枝梢害虫 (槐花球蚧 Eulecaniumkuwanai (Kanda) .&扁平球坚蚧 Parthenolecanium orientalis(Bouch) )。光肩星天牛种群呈下降趋势 ;木蠹蛾种群为上升趋势 ;槐花球蚧种群虽有下降趋势 ,但虫口密度依然较高 ;扁平球坚蚧在白蜡纯林中种群有逐年增长的趋势 ,而在混交林内数量变化平中有降。研究发现各害虫在合理的树种混交方式下 ,种群数量变化幅度小 ,危害轻 ,因而认为生产中只有营造合理树种搭配下的混交林才能防止和控制害虫的发生。

两个不同江豚群体ISSR遗传多样性初步分析

采用ISSR分子标记对中国水域隶属于不同江豚(Neophocaena phocaenoides)亚种的两个群体即长江群体和渤海群体的遗传多样性进行分析。用19条ISSR引物及3对引物组合对两个群体共36个样品的基因组DNA进行PCR扩增,共得到115个清晰的扩增位点,其中多态性位点48个,多态位点百分率(PPL)为41.71%。POPGENE分析结果表明:两个江豚群体的总体遗传多样性水平相对较低(He=0.1643;Ho=0.2413);长江群体的遗传多样性水平(He=0.1530;Ho=0.2223)稍

Sequence variations of the S7 ribosomal protein gene in primitive cyprinid fishes: Implication on phylogenetic analysis

Cyprinidae is the largest fish family in the world and contains about 210 genera and 2010 species. Appropriate DNA markers must be selected for the phylogenetic analyses of Cyprinidae. In present study, the 1st intron of the S7 ribosomal protein (r-protein) gene is first used to examine the relationships among cyprinid fishes. The length of the 1st intron obtained by PCR amplification ranges from 655 to 859 by in the 16 cyprinid species investigated, and is 602 by in Myxocyprinus asiaticus. Out of the alignment of 925 nucleotide sites obtained, the parsimony informative sites are 499 and occupy 54% of the total sites. The results indicate that the 1st intron sequences of the S7 r-protein gene in cyprinids are rich in informative sites and vary remarkably in sequence divergence from 2.3% between close species to 66.6% between distant species. The bootstrap values of the interior nodes in the NJ (neighbor-joining) and MP (most-parsimony) trees based on the present S7 r-protein gene data are higher than those based on cytochrome b and the d-loop region respectively. Therefore, the 1st intron sequences of the S7 r-protein gene in cyprinids are sensitive enough for phylogenetic analyses, and the 1st intron is an appropriate genetic marker for the phylogenetic reconstruction of the taxa in different cyprinid subfamilies. However, attempts to discuss whether the present S7 r-protein gene data can be applied to the phylogeny of the taxa at the level of the family or the higher categories in Cypriniformes need further studies.

Annealing study of carrier concentration in gradient-doped GaAs/GaAlAs epilayers grown by molecular beam epitaxy

We measured the carrier concentration distribution of gradient-doped GaAs/GqAlAs epilayers grown by molecular beam epitaxy before and after annealing at 600 degrees C, using electrochemical capacitance voltage profiling, to investigate the internal variation of transmission-mode GaAs photocathodes arising from the annealing process. The results show that the carrier concentration increased after annealing. As a result, the total band-bending energy in the gradient-doped GaAs emission layer increased by 25.24% after annealing, which improves the pbotoexcited electron movement toward the surface. On the other hand, the annealing process resulted in a worse carrier concentration discrepancy between the GaAs and the GaAlAs, which causes a lower back interface potential barrier, decreasing the amount of high-energy photoelectrons. (C) 2009 Optical Society of America

Rearrangeable nonblocking SOI waveguide thermooptic 4x4 switch matrix with low insertion loss and fast response

A rearrangeable nonblocking 4 x 4 thermooptic silicon-on-insulator waveguide switch matrix at 1.55-mu m integrated spot size converters is designed and fabricated for the first time. The insertion losses and polarization-dependent losses of the four channels are less than 10 and 0.8 dB, respectively. The extinction ratios are larger than 20 dB. The response times are 4.6 mu s for rising edge and 1.9 mu s for failing edge.

协同环境中共有资源的细粒度协作访问控制策略

在军事和商业领域中,由多个自治域形成的协作群体对共有资源(如客体、应用程序以及服务等)的访问问题越来越受到重视.协作中的基本事实是:尽管这些自治域有共同的目标,但同时有不同的自身利益.为了有效地保护共有资源,把“信任”的概念引入了协作访问控制中,并在基于量化权限的思想上,提出了细粒度的协作访问控制策略.在该策略里,权限的使用形式是元权限,也就是单位权限,它是访问共有客体权限的一个划分,可为多个域中不同用户所拥有.当访问共有资源时,参与者们所拥有的元权限的值之和以及人数必须达到规定的权限门限值和人数值,并且访问时间是所有参与者的共同许可访问时间段,这使得可以对协作资源进行有效地分布控制.另外,还引入了元权限的使用时间段约束.最后,证明了该细粒度协作访问控制策略关于协作系统的状态转换是保持安全的.

基于安全操作系统的电子证据获取与存储

基于实时取证的思想,提出了一种安全可取证操作系统(security forensics operating system,简称SeFOS)的概念和实现思路.提出了其总体结构,建立了该系统的取证行为模型,对其取证服务和取证机制进行了分析并作了有关形式化描述,阐述了证据数据的采集和安全保护方法,提出把取证机制置于内核,基于进程、系统调用、内核资源分配和网络数据等获取证据的方法,并通过模拟实验验证了SeFOS的可取证性.可取证操作系统的研究对于进一步研究可取证数据库管理系统(forensic database management system,简称FDBMS)和可取证网络系统(forensic network,简称FNetWork)具有重要意义.

针对特定几何语言的句法语义一体化分析方法

提出了一种句法语义一体化的语言分析方法,句法分析和语义理解时采用并行方法,利用两者之间的相互关系实现句法和语义的分析。针对自然语言理解在几何特定领域的约束性,以依存语法为基础,利用标注过的语料库知识,采用规则统计模型,对已经标注好词性语义的句子词串进行句法语义一体化分析,生成符合数学规范的数学表达式。实验证明,建立的系统对100个几何描述的句子进行测试,得到的正确率为98％,在几何领域具有良好的实用性,能够满足实际的需要。

金膜上亚波长周期性孔阵的模拟与研制

分析了980 nm波长的光在透过制作在金膜上的亚波长周期性孔阵时的透射增强现象.通过建立中心带缺陷孔的三角晶格的孔阵模型,并采用三维时域有限差分方法对该模型的透射情况进行模拟分析.结果表明通过优化孔阵周期参数可以对特定波长的光实现一定程度的选择透过性.当孔阵周期为450 nm,中心缺陷孔径为400 nm,孔阵中单个孔孔径为150 nm时,980 nm波跃光透过该孔阵时具有明显的透射增强效应,并且距孔阵表面3μm的远场光斑尺寸被局限在亚波长尺度(880 nm).研究了使用聚焦离子束在金膜上制备孔阵的工艺,成功研制了与没计尺寸一致的孔阵.这种孔阵可以集成在980 nm垂直腔面发射激光器上,用于改善器件的远场光学特性.

基于双边滤波和双树复小波的图像去噪算法

中国科学院