贵州省地萼苔科植物初步研究

根据文献记载以及对采自贵州省各县市地萼苔科Geocalycaceae植物标本(300余份)的鉴定,经统计贵州省地萼苔科植物现有18种l变种,其中中华裂萼苔Chiloscyphus sinensis、爽气裂萼苔C.fragrans为贵州新记录.根据各个种的形态特征,编制了该科的分种检索表,并对新记录种的主要形态特征进行了...     

高校搭建大学生科研创新平台的探索与实践——以福建师范大学经济学院为例

分析了我国高校开展学生课外学术科技创新工作的现状,结合福建师范大学经济学院的具体做法,就如何搭建大学生参与科研创新活动平台进行有针对性的分析与探索,为高校工作中如何提升大学生创新能力、科研能力提供了新的思路.     

岷江上游河谷土壤粒径分形维数及其影响因素

运用土壤体积粒径分维模型计算了岷江上游河谷土壤粒径分形维数,分析了分形维数的空间变化特点及其与粒度组成、粒度参数和铁游离度等之间的关系.土壤粒径分形维数空间分布与气候、植被环境有关.分形维数可以反映粒径大小.分形维数与粒度标准偏差和峰度不存在相关性,样品粒度特征主要受原位母质风化影响.铁游离度(Fed/Fet)与分形维...     

低温-秋水仙素诱导甜瓜多倍体研究

以刚展开子叶的甜瓜植株为材料,采用低温-秋水仙素处理,植株全部成活,通过检测气孔-叶绿体的变化情况,选出4株定植于营养箱内,采收全部植株所结果实,保留种子并测量.采收期过后,用嫩芽叶尖为材料,对3株甜瓜进行染色体计数检测,检出1个四倍体.结果表明:低温-秋水仙素处理可以有效降低秋水仙素的毒害作用,提高植株成活率.植株后期,有由四倍体回复到二倍体的现象,说明在植株生长后期倍性稳定性有所改变.     

变压器设计原则的探讨

变压器是指用来改变交流电压大小的一种电气设备。它是根据电磁感应的设计原理,把某一等级交流的电压变换成另一等级交流的电压,从而满足不同负荷的需要。变压器不论在工作还是在生活中都有非常重要的作用,而且越来越得到广泛的应用和推广。其安全可靠性也是变压器发展的最大瓶颈,因此变压器在电力系统、供用电系统等各大系统中都占有举足轻重的作用。文章就变压器的设计原则、原理特点进行一定的探讨。     

掺聚丙烯纤维对改善高强混凝土性能的研究

在高强混凝土逐渐被广泛应用的今天,改善高强混凝土的性能成为目前工程界亟需解决的问题,掺聚丙烯纤维就是改善高强混凝土性能的重要手段之一。作者介绍了聚丙烯纤维混凝土的发展历史,阐述了聚丙烯纤维对高强混凝土性能的改善及作用机理。     

浅谈危机管理

企业在生产经营中面临着多种危机,并且无论哪种危机发生,都有可能给企业带来致命的打击。对于企业来说,危机管理迫在眉睫,它不再是仅仅局限于处理突发性事件,而注重挖掘企业管理的深层次原因日渐成为企业管理必不可少的组成部分。     

汽轮机汽封改造

文章通过对迷宫梳齿密封与王常春接触式蜂窝汽封的优缺点和工作原理进行了比较说明,介绍了王常春接触式蜂窝汽封在汽轮机组上的应用情况,以及进行汽封改造后所取得的效果.     

The ribosome uses two active mechanisms to unwind messenger RNA during translation

The ribosome translates the genetic information encoded in messenger RNA into protein. Folded structures in the coding region of an mRNA represent a kinetic barrier that lowers the peptide elongation rate, as the ribosome must disrupt structures it encounters in the mRNA at its entry site to allow translocation to the next codon. Such structures are exploited by the cell to create diverse strategies for translation regulation, such as programmed frameshifting, the modulation of protein expression levels, ribosome localization and co-translational protein folding. Although strand separation activity is inherent to the ribosome, requiring no exogenous helicases, its mechanism is still unknown. Here, using a single-molecule optical tweezers assay on mRNA hairpins, we find that the translation rate of identical codons at the decoding centre is greatly influenced by the GC content of folded structures at the mRNA entry site. Furthermore, force applied to the ends of the hairpin to favour its unfolding significantly speeds translation. Quantitative analysis of the force dependence of its helicase activity reveals that the ribosome, unlike previously studied helicases, uses two distinct active mechanisms to unwind mRNA structure: it destabilizes the helical junction at the mRNA entry site by biasing its thermal fluctuations towards the open state, increasing the probability of the ribosome translocating unhindered; and it mechanically pulls apart the mRNA single strands of the closed junction during the conformational changes that accompany ribosome translocation. The second of these mechanisms ensures a minimal basal rate of translation in the cell; specialized, mechanically stable structures are required to stall the ribosome temporarily. Our results establish a quantitative mechanical basis for understanding the mechanism of regulation of the elongation rate of translation by structured mRNAs.     

Genetic variants in novel pathways influence blood pressure and cardiovascular disease risk

Blood pressure is a heritable trait influenced by several biological pathways and responsive to environmental stimuli. Over one billion people worldwide have hypertension (≥140?mm?Hg systolic blood pressure or ≥90?mm?Hg diastolic blood pressure). Even small increments in blood pressure are associated with an increased risk of cardiovascular events. This genome-wide association study of systolic and diastolic blood pressure, which used a multi-stage design in 200,000 individuals of European descent, identified sixteen novel loci: six of these loci contain genes previously known or suspected to regulate blood pressure (GUCY1A3-GUCY1B3, NPR3-C5orf23, ADM, FURIN-FES, GOSR2, GNAS-EDN3); the other ten provide new clues to blood pressure physiology. A genetic risk score based on 29 genome-wide significant variants was associated with hypertension, left ventricular wall thickness, stroke and coronary artery disease, but not kidney disease or kidney function. We also observed associations with blood pressure in East Asian, South Asian and African ancestry individuals. Our findings provide new insights into the genetics and biology of blood pressure, and suggest potential novel therapeutic pathways for cardiovascular disease prevention.