Effect of synthesis temperature on density and microstructure of MgB2 superconductor at ambient pressure

The experimental thermodynamic of MgB₂ synthesis process and phase compositions have been investigated by diffraction thermal analysis (DTA) technology and X-ray diffraction. The fabrication of MgB₂ bulks and superconducting properties at the temperatures range from 600 to 800°C were reported. And microstructure of MgB₂ bulks were observed by scanning electron microscope (SEM). A method was developed to determine the porosity of MgB₂ and the highest density can be obtained in MgB₂ prepared at 650°C at ambient pressure. It is found that the vapor pressure of Mg increases remarkably at high temperature, leading to the high porosity in MgB₂ samples. MgB₂ bulk with good superconducting property and fine microstructure was synthesized at 750°C.     

高压输电线路铁塔选型漫谈

本文结合近几年来,我国高压输电线路铁塔选型方面的基本情况,和作者本人从事高压输电线路铁塔结构设计中的一些经验和看法,简述了大负荷、新结构的塔型使用现状和铁塔选型应注意的一些问题。     

小流量灰浆泵组合密封设计

用于输送含有细小颗粒流体的小流量（0．5～5t／h）氢氧化钙浆液泵的机械密封，极易被溶液中含有的固体颗粒磨损而丧失密封性能。针对这一问题，提出了一种背叶片加上橡胶波纹管机械密封组合的密封结构，并辅之以溢流结构来保护电机，从而解决了灰浆泵的密封问题，延长了泵的使用寿命，使泵装置的体积大大缩小，且易于维修。本文阐述了这种组合密封结构的原理及尺寸设计。     

自蔓延高温合成材料中耗散结构及研究意义

在简介自蔓延高温合成技术和耗散结构论的基础上,分析和阐述了自蔓延高温合成材料中的耗散结构,探讨了自蔓延高温合成材料中耗散结构的研究意义。     

电荷束团非均匀密度分布引起的发射度增长

直线加速器中电荷束团的非线性效应是导致束流发射度增长的一个重要原因。文中给出了直线加速器中几种常见的非均匀密度分布的有限长空间电荷束团所具有的非线性自场能，即纵向非均匀电荷密度分布分别为水袋型，抛物线型，而横向密度分布为均匀型，水袋型，抛物线型及高期型等各种组合非均匀密度分布的自场能公式，并得到了由束团非线性的均匀电荷密度分布引起的束流发射度增长。     

矿热炉把持器的传热分析

以矿热炉电极把持器的传热计算为核心,研究把持器的结构设计和参数选用。通过对冷却水流量、壁面厚度、水垢厚度、烟气温度等影响因素的研究,结合把持器传热边界条件,分析了在不同参数条件下传热变化趋势,为电极把持器的设计和应用提供了参考依据。     

Role of ERAB/L-3-hydroxyacyl-coenzyme A dehydrogenase type II activity in Abeta-induced cytotoxicity

Endoplasmic reticulum-associated amyloid beta-peptide (Abeta)-binding protein (ERAB)/L-3-hydroxyacyl-CoA dehydrogenase type II (HADH II) is expressed at high levels in Alzheimer's disease (AD)-affected brain, binds Abeta, and contributes to Abeta-induced cytotoxicity. Purified recombinant ERAB/HADH II catalyzed the NADH-dependent reduction of S-acetoacetyl-CoA with a Km of approximately 68 microM and a Vmax of approximately 430 micromol/min/mg. The contribution of ERAB/HADH II enzymatic activity to Abeta-mediated cellular dysfunction was studied by site-directed mutagenesis in the catalytic domain (Y168G/K172G). Although COS cells cotransfected to overexpress wild-type ERAB/HADH II and variant beta-amyloid precursor protein (betaAPP(V717G)) showed DNA fragmentation, cotransfection with Y168G/K172G-altered ERAB and betaAPP(V717G) was without effect. We thus asked whether the enzyme might recognize alcohol substrates of which the aldehyde products could be cytotoxic; ERAB/HADH II catalyzed oxidation of a variety of simple alcohols (C2-C10) to their respective aldehydes in the presence of NAD+ and NAD-dependent oxidation of 17beta-estradiol. Addition of micromolar levels of synthetic Abeta(1-40) to purified ERAB/HADH II inhibited, in parallel, reduction of S-acetoacetyl-CoA (Ki approximately 1.6 microM), as well as oxidation of 17beta-estradiol (Ki approximately 3.2 microM) and (-)-2-octanol (Ki approximately 2.6 microM). Because micromolar levels of Abeta were required to inhibit ERAB/HADH II activity, whereas Abeta binding to ERAB/HADH II occurred at much lower concentrations (Km approximately 40-70 nM), the latter more closely simulating Abeta levels within cells, Abeta perturbation of ERAB/HADH II was likely to result from mechanisms other than the direct modulation of enzymatic activity. Cells cotransfected to overexpress ERAB/HADH II and betaAPP(V717G) generated malondialdehyde-protein and 4-hydroxynonenal-protein epitopes, which were detectable only at the lowest levels in cells overexpressing either ERAB/HADH II or betaAPP(V717G) alone. Generation of such toxic aldehydes was not observed in cells contransfected to overexpress Y168G/K172G-altered ERAB and betaAPP(V717G). We conclude that the generalized alcohol dehydrogenase activity of ERAB/HADH II is central to the cytotoxicity observed in an Abeta-rich environment.     

空气污染排放视角下中国核电的健康效益

核电在改善空气质量方面具有重要的作用。本文对比了核电与煤电的空气污染物排放系数,根据空气污染物引起的死亡率与人均燃煤发电量的负指数幂关系,评估了中国通过发展核电在改善空气质量方面对居民的健康效益,并对未来的健康效益进行了分析。结果显示,发展核电能够避免的死亡人数在增加。据估算,1995—2018年,中国核电累计可避免约4.7万人因空气污染物死亡,可避免约22.6万人因空气污染物患病。2020—2030年,预计会避免8.3万~9.4万人死亡,避免39.7万~45.1万人患病。     

Nitrogen utilization and transformation in red soil fertilized with urea and ryegrass

The influence of fertilization with urea and ryegrass on nitrogen utilization and transformation in red soil has been studied by using ^15N tracer method.When urea and ryegrass were applied alone or in combination,the percentage of N uptaken by ryegrass from labelled urea was 3 and 1.7 times that from labelled ryegrass for the application rate of 200mgN.kg^-1 and 100mgN.kg^-1,respectively;combining application of ryegrass and ureareduced uptake of urea N and increased uptake of ryegrass N by ryegrass plant,but the percentage of N residued in soil increased for urea and decreased for ryegrass.when urea and ryegrass were applied alone,the percentage of N residued in soil from labelled ryegrass was more than 69% while that from labelled urea was less than 25%,and much more ryegrass N was incorporated into humus than urea N.