不同体积分数二甲基亚砜对DNA变性的影响

利用原子力显微镜和动态光散射研究不同体积分数二甲基亚砜(DMSO)对质粒及线性DNA变性的影响。结果表明,体积分数1%的DMSO也能导致DNA发生局部变性,这个结果可以用原子力显微镜直接观测。同时,由于质粒DNA连接数的守恒以及DNA单链的产生,通过原子力显微镜和动态光散射发现,DNA随DMSO体积分数的增加逐渐形成超螺旋结构,DNA聚拢程度增加;DMSO体积分数从0增加到10%时,pBR322 DNA、5 000 bp DNA及λ-DNA的平均粒径分别从(474±10) nm、(554±11) nm和(871±17) nm降低到(257±8) nm、(282±18) nm和(449±21) nm。     

Cell lineage-specific undermethylation of mouse repetitive DNA

Several distinct cell lineages are established during mouse embryogenesis. The trophectoderm and primitive endoderm give rise to extraembryonic structures alone, while the primitive ectoderm becomes the fetus proper. Recent studies suggest that the levels of DNA modification are lower in inactive X chromosomes from extraembryonic tissues than in embryonic and adult somatic tissues. Using HpaII/MspI isoschizomers, Southern blots and cloned probes, we show here that repetitive DNA sequences from all derivatives of the two extraembryonic lineages, trophectoderm and primitive endoderm, are substantially undermethylated compared with primitive ectoderm derivatives. This contrasts with the highly methylated state of these repetitive elements observed in adult somatic tissues. Specific demethylation or inhibition of de novo methylation, or a combination of both mechanisms, may be involved. These findings suggest that elements of gene regulation dependent on DNA modification may be different in extraembryonic cell lineages.     

Aberrant DNA methylation patterns in cultured mouse embryos

Mouse early embryos undergo genome-wide demethylation and remethylation events during pre-implantation development. Abnormal methylation reprogramming is thought to be associated with development arrest. Using immunofluorescence staining with an antibody against 5-methylcytosine (MeC), we examined the genome methylation patterns of mouse embryos cultured in vitro. The results did not show the difference in staining patterns between development-blocked two-cell embryos that cultured in vitro and the two-cell embryos that were freshly collected from the donor mice. But in vitro-arrested morulae displayed a strong positive staining when compared to the morulae freshly collected from the donor mice. At the blastocyst stage, although most embryos showed the expected methylation patterns, with highly stained inner cell mass (ICM) and weekly stained trophectoderm (TE), a proportion of embryos were dimly stained in both ICM and TE. These results indicated that the methylation profile of the embryos could be changed by culturing in vitro when the embryos were in the transition from morulae to blastocyst.     

Clifford对应的推广

设H为任意有限群G的一个次正规子群，θ为H的一个不可约复特征标．文章证明了若特征标对(H，θ)在G中满足共轭封闭性，则特征标的诱导可定义一个双射：Irr(T|θ)→Irr(G|θ)，ξ|ξ^G，其中T=IG(H，θ)为该特征标对在G中的惯性群．此外，定理还推广了著名的Clifford对应以及Isaacs在1984年提出的极大Fn-对应．     

Representations of and translation between common fractions and decimal fractions

Recent years have seen a boom in research on the magnitude representations of common fractions and decimal fractions. However, previous studies generally only explored the magnitude representations of these two types of fractions in isolation. The present study, using a pretest-training-posttest design, examined and compared the magnitude representations of both types of fractions, and more importantly examined their relations to fraction translation and overall mathematical competence. The results showed that （1） accurate magnitude representations developed more often for decimal fractions than for common fractions; （2） individual differences in fraction magnitude representations predicted individual differences in fraction translation performance above and beyond initial knowledge of fraction translation; （3） mere exposure to visual representations of fractions on number lines im- proved children＇s mental representations of fraction magnitudes more than exposure to visual representations of fractions on cir- cles or reading a textbook section on fractions. The present findings suggest that, like whole numbers, both types of fractions are organized on a mental number line, which appears to provide a central conceptual structure for organizing a wide range of numer- ical knowledge. Educational implications of the findings are discussed.     

学术不端行为举报

河南农业大学机电工程学院教师王向中2010年3月7日向《科技导报》投来稿件“在氯化胆碱离子液体润滑条件下铜一钢摩擦副的摩擦学性能研究”。     

双重接力棒式通信

以铁道监测系统为例,详细地介绍了一种技巧性的数据通信方法, 实现了对数据量大、数据类型多变、速度和精度要求高、采集点不固定的数据的灵活高速采集.     

学术不端行为举报

广东省惠州学院化学工程系罗付生和江西省环境保护科学研究院汪青梅发表在《高分子材料科学与工程》2007年第23卷第1期第109￣111页(转116页)的论文"硬沥青对     

学术不端行为举报

举报信箱E-mail:hjy@cast.org.cn举报一中国海洋大学生命科学与技术学部谢正侠、慕永通、王芸发表在《中国海洋大学学报》(社会科学版)2007年第3期第9-13页的论文"水     

学术不端行为举报

中国科学院上海有机化学研究所原博士生黄凌琳等于2006年发表在《美国化学会志》(Journal of the American Chemical Society)第128卷,第5624页到第5625页的论文     

真分数表成单位分数和的一类特解

用初等的方法研究了m/n表法，并给出了真分数表成单位分数和的一类特解。