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...     

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。     

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.     

Oxysterols direct immune cell migration via EBI2

Epstein-Barr virus-induced gene 2 (EBI2, also known as GPR183) is a G-protein-coupled receptor that is required for humoral immune responses; polymorphisms in the receptor have been associated with inflammatory autoimmune diseases. The natural ligand for EBI2 has been unknown. Here we describe the identification of 7α,25-dihydroxycholesterol (also called 7α,25-OHC or 5-cholesten-3β,7α,25-triol) as a potent and selective agonist of EBI2. Functional activation of human EBI2 by 7α,25-OHC and closely related oxysterols was verified by monitoring second messenger readouts and saturable, high-affinity radioligand binding. Furthermore, we find that 7α,25-OHC and closely related oxysterols act as chemoattractants for immune cells expressing EBI2 by directing cell migration in vitro and in vivo. A critical enzyme required for the generation of 7α,25-OHC is cholesterol 25-hydroxylase (CH25H). Similar to EBI2 receptor knockout mice, mice deficient in CH25H fail to position activated B cells within the spleen to the outer follicle and mount a reduced plasma cell response after an immune challenge. This demonstrates that CH25H generates EBI2 biological activity in vivo and indicates that the EBI2-oxysterol signalling pathway has an important role in the adaptive immune response.     

采用决策树分类方法进行煤矸石信息提取研究

利用遥感技术快速、准确地调查煤矸石堆分布情况,对预防地质灾害以及保护生态环境和居民生命财产安全有着重要的指导意义.基于TM多光谱影像,运用知识决策树分类方法对江西萍乡煤矿区进行煤矸石信息提取试验.首先,在研究区背景知识的基础下,统计分析矿区内煤矸石及其他典型地物在影像上的光谱特征,建立了研究区的分类知识库;其次,在决策...     

共沉淀-熔融法制备铁磁性微晶玻璃及其表征

采用SiO2-Na2O-CaO-P2O5-Fe2O3五元系统通过共沉淀-熔融法制备铁磁性微晶玻璃,利用XRD确定其晶相并计算晶体的晶格常数和晶粒尺寸,采用振动样品磁强计(VSM)测试样品的磁性能.结果证明,玻璃液在自然冷却的过程中形成了大量的磁铁矿,不需要热处理过程即可获得具有磁铁矿唯一晶相的铁磁性微晶玻璃,其比饱和磁矩为36.74 A.m2/kg,矫顽力为27 kA/m.     

基于事例推理系统中检索策略的分析与研究

讨论了基于事例推理(CBR)在人工智能系统中的作用,分析了常用的CBR检索算法,并着重研究了提高系统检索效率问题.针对CBR系统的关键性问题事例检索,提出了一种分级检索算法与最近相邻算法相结合的检索策略(L&NCBR),分析了在精确匹配与非精确匹配情况下该策略的效率,并给出了基于L&NCBR的智能推理系统运行情况分析.结果表明L&NCBR策略在提高系统检索的稳定性和效率方面是有效的.     

考虑后悔规避的风储联合参与日前市场竞标策略

为应对风储联合参与日前市场竞标的风险,减弱决策者的后悔心理,提出了一种考虑后悔规避的风储联合参与日前市场竞标策略.采用蒙特卡洛法将风电出力、市场电价的随机模型转化为多概率场景的确定模型;在日前市场竞标阶段,引入后悔度指标描述风储联合系统的后悔心理,同时考虑实时市场的不平衡结算因素,以最小-最大后悔度为优化目标,建立风储...