Dynamic recrystallization induced by plastic deformation at high strain rate in a Monel alloy

An investigation has been made into the plastic deformation behavior of a Monel alloy deformed at high strain rate of 10(5) s(-1) by split Hopkinson bar. The results reveal that there are some equiaxed grains with an average size of 150 nm in diameter in the center of the shear bands, suggesting that this microstructure characteristics be developed by dynamic recrystallization, arising from the deformation and the rapid temperature rise in the band. Analysis shows that the plastic strain rate and the mobile dislocation density play a key role in the new crystallized grain formation and growth. Based on grain boundary energy change and diffusion mechanism, the grain growth kinetics is developed for plastic deformation at a high strain rate.

12种鳃形目鱼类mt DNA NI4 L- NI4基因的序列变异及其分子系统学

鳃形目鱼类是一类在鱼类乃至脊椎动物进化史上占有很重要地位的古老濒 危鱼类，长期悬而未决的系统演化关系为世人瞩目.采用DNA测序技术首次测定了 包括中国特有鳃形目鱼类在内的12种鳃形目鱼类的mtDNA ND4L和ND4基因(703 by)的序列，并进行了分子系统学分析.从分子系统学的角度得出了如下结论:(1) 鲤属可以归并到鳃属;(2)达氏鳃与中华鳃的亲缘关系最近，很有可能为中华鳃的 一陆封类型;(3)环太平洋地区的鳃科鱼类可能有共同的起源;(4) ND4L和ND4基 因是进行鳃形目鱼类系统演化研究很好的遗传标记.

CO_2浓度对中肋骨条藻的光合无机碳吸收和胞外碳酸酐酶活性的影响

为探讨低光照(30 μmol·m-2·s-1)和高光照(210 μmol·m-2·s-1)条件下海水CO2浓度变化对海产硅藻中肋骨条藻(Skeletonema costatum)的生理影响,对该藻生长及其光合CO2吸收和胞外碳酸酐酶(CAext)活性进行了测定,结果表明,在低光条件下,CO2浓度变化(4～31μmol/L CO2)对该藻的生长和净光合速率的影响比高光条件大.CAext在12和31μmol/L CO2时没有检测出活性;但在4 μmol/L CO2时则有明显活性,且其高光条件下的活性是低光条件

Micro-raman investigation of defects in a 4H-SiC homoepilayer

Three types of defects, namely defect I, defect 11, defect 111, in the 4H-SiC homoepilayer were investigated by micro-raman scattering measurement. These defects all originate from a certain core and are composed of (1) a wavy tail region, (11) two long tails, the so called comet and (111) three plaits. It was found that there are 3C-SiC inclusions in the cores of defect 11 and defect III and the shape of inclusion determines the type of defect II or defect III. If the core contains a triangle-shaped inclusion, the defect III would be formed; otherwise, the defect 11 was formed. No inclusion was observed in the core of the defect I. The mechanisms of these defects are discussed.

MutS蛋白识别DNA错配机制的研究

DNA生物合成过程中DNA聚合酶会错误的掺入一些碱基而导致错配，这些错配的碱基如果不能被及时地更正将会引起机体广泛的突变。DNA错配修复系统正是基于这样一种需要而产生的，它能够切除含有错配的DNA片段并重新合成出一段正确的DNA，因此对于维持基因组的稳定性具有重要的意义。 大肠杆菌DNA错配修复系统包含11种蛋白活性，并可分为起始、切割和修复三个阶段。起始阶段的第一个步骤是错配识别，这一功能是由一种叫作MutS的蛋白来完成的，它能够特异性的识别并且结合到错配上，然后引发下游一系列的修复反应。为了更深入的理解MutS蛋白识别镶嵌在随机DNA序列中的错配的机制，我们纯化了MutS及其突变体蛋白，构建了一个2279 bp的在1/4位置带有G/T错配的DNA片段和一个具有同样长度与序列的完全配对的DNA片段，然后在原子力显微镜下观察MutS及突变体蛋白与这两种DNA底物的作用方式。结果表明MutS蛋白不但能与错配的DNA结合也能与完全配对的DNA结合，而且MutS蛋白能够诱导这两种DNA底物形成一种形似a字母的环状结构，在这种结构中MutS蛋白位于两条DNA臂的交叉处。我们发现这些环状结构是在MutS蛋白寻找错配的过程中形成的，因为随着时间推移越来越多的错配位点会被MutS蛋白占据。这些结果表明MutS蛋白非特异性的结合到DNA上，然后诱导DNA形成a环状结构，并且凭借a环结构的形成对DNA的两条臂同时进行扫描以便寻找出错配的碱基对。根据以上结果我们推测a环模式是MutS蛋白寻找错配的一种机制。这些研究也为用单分子的手段研究蛋白与DNA的相互作用提供了一种可行的方法。

CSR外靶实验终端大型探测器读出电子学研制

兰州重离子加速器-冷却储存环外靶实验终端大型探测器中子墙和TOF墙分别共有504个和360个通道用于测量中子和带电粒子的飞行时间,需要高精度时间测量的读出电子学系统。研制的8通道读出电子学模块采用了前沿定时的时间测量方法、基于TOT技术的电荷测量方法和PXI总线平台,电子学测试结果显示时间测量精度好于25ps。

醋酸酯淀粉包膜尿素水中养分溶出特征

以研制的4种醋酸酯淀粉包膜尿素肥料为研究对象,日本70 d聚烯烃包膜尿素肥料为对照,研究醋酸酯淀粉包膜尿素在水中尿素态氮溶出特征,以确定醋酸酯淀粉包膜尿素的控释性能。结果表明,醋酸酯淀粉包膜肥料尿素累积溶出曲线呈倒"L"型,在水中7~13 d达到最大溶出量,尿素态氮累积溶出80%的时间为2~3 d,初期溶出率65.71%~75.79%;养分累积释放率不超过75%的时间为1~2 d;第7 d微分溶出率都显著大于2.5%。聚烯烃包膜肥料尿素态氮累积溶出80%的时间超过40 d,初期溶出率为2.05%;聚烯烃养分累积释放率36 d为73.32%,37 d为75.01%;第7 d微分溶出率1.68%。醋酸酯淀粉包膜尿素缓/控释效果较差,对养分的控释能力明显低于聚烯烃包膜尿素,但对尿素态氮起到了一定的缓/控释作用。醋酸酯淀粉包膜尿素及聚烯烃包膜尿素肥料在水中尿素态氮累积溶出特征曲线符合一元二次方程模型。

Triblock poly(lactic acid)-b-poly(ethylene glycol)-b-poly(lactic acid)/paclitaxel conjugates: Synthesis, micellization, and cytotoxicity

A triblock poly(lactic acid)-b-poly(ethylene glycol)-b-poly(lactic acid) (PLA-PEG-PLA)/paclitaxel (PTX) conjugate was synthesized by the reaction of carboxyl-terminated copolymer PLA-PEG-PLA with PTX in the presence of dicyclohexylcarbodiimide and dimethylaminopyridine. Carboxyl-terminated copolymer PLA-PEG-PLA was prepared by the reaction of the hydroxyl end groups in copolymer PLA-PEG-PLA with succinic anhydride. Its structure was confirmed by NMR and gel permeation chromatography. The PLA-PEG-PLA/PTX conjugates could self-assemble into micelles in aqueous solutions with a low critical micelle concentration. Dynamic light scattering and environmental scanning electron microscopy analyses of the PLA-PEG-PLA/PTX micelles revealed their spherical structure and size of 220 nm. The antitumor activity of the conjugate against woman Hela cancer cells, evaluated by the 3-(4,5-dimethylthiazol2-yl)-2,5-diphenyl tetrazolium bromide method, showed that the conjugates had an antitumor activity similar to that of pure PTX. The obtained PLA-PEG-PLA/PTX conjugates are expected to be used in clinical practice.