非对称广义正定矩阵定义的再推广

对常规的正定矩阵的定义进行了再推广，由此得出非对称的广义正定矩阵及一些结果。     

A general method for site-directed mutagenesis in prokaryotes

The genetic analysis of genes from prokaryotic species for which experimental genetic systems have not yet been developed is often limited by the difficulty of producing mutations in those genes. We report here a general technique applicable to Gram-negative prokaryotes for site-directed mutagenesis of cloned DNA fragments which we have applied to the study of the symbiotic nitrogen fixation genes of Rhizobium meliloti. In particular, we mutagenized cloned R. meliloti restriction fragments in Escherichia coli with transposon Tn5 and then replaced the wild-type parental DNA sequences with the mutant DNA sequences in the R. meliloti genome. Using this method we show that an R. meliloti DNA restriction fragment, cloned previously on the basis of homology to Klebsiella pneumoniae nif genes, contains gene(s) essential for symbiotic nitrogen fixation. In addition, we use this method to construct a physical genetic map of a subset of the R. meliloti nif genes.     

A New Definition of Virus

Security experts have not formally defined the distinction between viruses and normal programs. The paper takes user＇s intension as the criteria for malice, gives a formal definition of viruses that aim at stealing or destroying files, and proposes an algorithm to detect virus correctly. Compared with traditional definitions, this new definition is easy to understand, covers more malwares, adapts development of virus technology, and defines virus on the spot. The paper has also analyzed more than 250 real viruses and finds that they are all in the domain of the new definition, this implies that the new definition has great practical significance.     

Proximity代数的一种合理定义

将经典拓扑中的Proximity空间论基础合理地推广到伪补格上,在一般伪补格L上建立了一种较为合理的Poximity结构以形成“（半）Proximity代数”,并且就合理性问题与几个作者给出的格上Proximity结构进行了比较。     

模糊极限的一种新定义

在模糊分析中模糊极限的定义都是基于扩张原理的形式给出的,并且都是对元素遍历某个条件或取λ遍历[0,1]所对应的全体结果进行运算,这种运算中的遍历过程给模糊极限的定义形式及其应用带来了极大的不便。利用模糊结构元方法给出了模糊极限的一种新的定义,这种形式摒弃了对元素遍历的繁琐运算,使得该定义运用起来更加灵活简便,而且也体现了模糊结构元方法在简化模糊分析计算方面的优越性。最后给出了 3 个结论,即极限的加减法与数乘定理、极限唯一性定理、有界性定理,     

关于混沌的Devaney定义的一点注记

说明了Ｄｅｖａｎｅｙ的混沌定义中的拓扑传递性和初值敏感依赖性之间的一些联系，证明了在拓扑传递条件满足时，加一上些不太强的条件后，初值敏感依赖性满足。     

A new definition of restricted Lie superalgebras

A new definition of restricted Lie superalgebras has been given; some important results on the representation theory of restricted Lie superalgebra have been obtained.     

A unifying model for the G1 period in prokaryotes and eukaryotes

A model to explain the cell division cycle in both prokaryotes and eukaryotes is presented. No specific 'G1 functions' take place during the G1 period, which is merely part of a larger period for the preparation of DNA synthesis which began at the previous initiation of DNA synthesis. A G1 period exists merely because the doubling time of the cells is greater than the sum of the S and G2 periods.     

论山区概念的法律界定

山区可持续发展立法已成为全新的世界性发展趋势，我国学者提出制定一部《山区法》或《山区资源综合开发与保护法》。构建山区可持续发展的法制体系，先要确定山区概念并划分其范围。文章通过综合学者从自然科学和人文社会科学角度所作出的定义，提出我国在法律角度对山区定义的缺陷，借鉴国外山区法中对山区进行定义中所采用的各种标准，结合我国山区的特殊性对其做出界定是最科学的。     

一种高清帧内预测单元快速选择算法

针对高效视频编码标准提出一种CU划分快速终止算法.该算法选择图像纹理复杂度作为特征向量,将HEVC帧内预测与k-means聚类方法相结合,通过每种尺寸CU的聚类中心减少率失真优化的次数,提前终止CU块的划分,在达到降低编码复杂度的同时依然保持较好的编码效率.测试结果表明,本算法与参考算法HM10.0相比较,视频图像质量基本不变,而编码时间大幅减少.     

Deep sub-seafloor prokaryotes stimulated at interfaces over geological time

The sub-seafloor biosphere is the largest prokaryotic habitat on Earth but also a habitat with the lowest metabolic rates. Modelled activity rates are very low, indicating that most prokaryotes may be inactive or have extraordinarily slow metabolism. Here we present results from two Pacific Ocean sites, margin and open ocean, both of which have deep, subsurface stimulation of prokaryotic processes associated with geochemical and/or sedimentary interfaces. At 90 m depth in the margin site, stimulation was such that prokaryote numbers were higher (about 13-fold) and activity rates higher than or similar to near-surface values. Analysis of high-molecular-mass DNA confirmed the presence of viable prokaryotes and showed changes in biodiversity with depth that were coupled to geochemistry, including a marked community change at the 90-m interface. At the open ocean site, increases in numbers of prokaryotes at depth were more restricted but also corresponded to increased activity; however, this time they were associated with repeating layers of diatom-rich sediments (about 9 Myr old). These results show that deep sedimentary prokaryotes can have high activity, have changing diversity associated with interfaces and are active over geological timescales.     

Genomic and functional adaptation in surface ocean planktonic prokaryotes

The understanding of marine microbial ecology and metabolism has been hampered by the paucity of sequenced reference genomes. To this end, we report the sequencing of 137 diverse marine isolates collected from around the world. We analysed these sequences, along with previously published marine prokaryotic genomes, in the context of marine metagenomic data, to gain insights into the ecology of the surface ocean prokaryotic picoplankton (0.1-3.0?μm size range). The results suggest that the sequenced genomes define two microbial groups: one composed of only a few taxa that are nearly always abundant in picoplanktonic communities, and the other consisting of many microbial taxa that are rarely abundant. The genomic content of the second group suggests that these microbes are capable of slow growth and survival in energy-limited environments, and rapid growth in energy-rich environments. By contrast, the abundant and cosmopolitan picoplanktonic prokaryotes for which there is genomic representation have smaller genomes, are probably capable of only slow growth and seem to be relatively unable to sense or rapidly acclimate to energy-rich conditions. Their genomic features also lead us to propose that one method used to avoid predation by viruses and/or bacterivores is by means of slow growth and the maintenance of low biomass.     

行列式的递归定义

采用归纳法的方法来定义n阶行列式，证明出定理1，并在此基础上证明出行列式的诸条性质．     

关于离散参数曲线网上曲率的一种刻画

针对由参数曲线网形成的四边形网格,提出了一种简洁快速的加细方法,即在保持初始网格不变的情况下,使每一个小极限曲面片为C2,而整体极限曲面为一次连续的.应用该方法,给出了一种四边形网格上任意顶点处的离散估计值的定义方法,主要包括离散的Gauss曲率和平均曲率的定义.最后,实验验证表明了该方法的有效性和优越性.     

侧间隙的一个新定义——双螺杆几何学的研究

在双螺杆几何学的研究中, 存在于两螺杆间的间隙是一个重要的概念。文中对同向旋转双螺杆的侧间隙作了新的定义, 并建立了它的数学模型, 推导了其计算公式, 证明了侧间隙的不均匀性