大型汽轮发电机的若干力学问题

本文对大型火力发电设备中的汽轮发电机设计与制造及运行中的若干力学问题作一简要的评述.列举了下述题目:(1)转子及轴系的振动问题;(2)定子铁芯及其支撑力学;(3)定子绕组端部振动问题;(4)发电机转子护环的强度;(5)发电机整机静动态力学特性与响应;(6)大件运输中的力学问题.     

“伯努利升力原理”批判

我的瑞典朋友马丁·宋贝先生于1953-1983年长期担任瑞典航空研究院(FFA)低速气动力部主任.他是一名至今还开飞机上天的有54年历史的老飞行员.这两年他常和我讨论飞机升力产生原理的传统说法,他认为许多人误用了伯努利定理来解释升力.他说:长达半个世纪,遍布全世界的飞行员教材中的错误概念,已经酿成了飞行事故,他有责任为此进行斗争.退体后的这几年,他东奔西跑到处说服人们接受他的意见,先是在 FFA内有了市场,接着欧洲民航年会(ECAC)采纳了他的批评,现在他又在争取国际民航组织(ICAO)和美国联邦航空局(FAA)纠正错误.不久前他寄给我一篇用英文写成的“檄文”,希望我帮助征求中国同行的意见.我将它翻译整理并加了标题“伯努利升力原理批判”介绍给大家.我觉得这篇文章涉及到科学原理的准确表述和科学普及的通谷解释的关系问题.飞机为什么能飞?或升力怎么产生的?这既是航空空气动力学要研究的课题,也是科普教育要回答的问题.文章所批判的说法在我国的科普读物、中学教材、飞行员课程、航空概论中也都采用,因为其通俗易懂,当然在真正的高等空气动力学教程中又是另外的讲法.关键是通俗解释不应当引入错误的概念,更不应当因错误概念导致危险的...     

Production of Charged Heavy Quarkonium-Like States at the LHC and Tevatron

We study prompt hadroproduction of the charged bottomonium-like states Zb± （10610） and Zb±（10650）, and the charged eharmonium-like states Zc± （3900） and Zc± （4020）, at the Tevatron and the LHC, provided that these states are S-wave hadronic molecules. Using two Monte Carlo event generators, Herwig and Pythia, to simulate the production of heavy meson pairs, we derive an order-of-magnitude estimate of the production rates for these four particles. Our estimates yield a cross section at the nb level for the Zb（10610） and Zb（10650）. The results for the Zc（3900） and Zc （4020） are larger by a factor of 2~30. These cross sections are large enough to be observed, and measurements at hadron colliders in the future will supplement the study using electron-positron collisions, and therefore allow to explore the mysterious nature of these exotic states.     

新疆14个地州市疾病预防与控制机构服务能力综合评价研究

本文利用主成分分析方法,借助SPSS统计软件建立评价模型,综合评价新疆14个地(州、市)疾病预防控制机构的服务能力进行了综合评价,研究结果提示:新疆14个地(州、市)级疾病预防控制机构中,综合服务能力位列前三位的分别是克拉玛依市、乌鲁木齐市和伊犁哈萨克自治州,位列后三位的分别是克孜勒苏柯尔克孜自治州、和田地区和喀什地区疾病预防控制中心,整体实力北疆地区机构优于南疆地区。     

超高压液相色谱荧光检测法快速测定水中痕量苯胺与联苯胺

建立了直接进样/超高压液相色谱荧光检测法快速分析水中苯胺和联苯胺的新方法。通过研究流动相、水样pH值、水样电导率和滤器材质的影响,确定了最优化的实验方案。水样直接通过0.22μm微孔滤膜(聚四氟乙烯材质)过滤,以乙腈-3.85 g/L醋酸铵(25∶75)为流动相,荧光检测器(苯胺λex/λem=232nm/329 nm,联苯胺λex/λem=292 nm/383 nm)在0.8 min内完成分析。苯胺和联苯胺在1.0～100.0μg/L范围内线性关系良好,相关系数均大于0.999,仪器精密度(n=10)分别为0.4%和0.5%,方法检出限(S/N=3)分别为0.023μg/L和0.024μg/L,方法定量下限(S/N=10)为0.078μg/L和0.079μg/L,方法回收率为86%～106%。该方法具有前处理简单、方法检出限低、分析速度快等优点,适用于水体中苯胺和联苯胺的快速检测。     

Electrochemical synthesis of magnetic iron oxide nanoparticles with controlled size

We present a novel and facile method enabling synthesis of iron oxide nanoparticles, which are composed mainly of maghemite according to X-ray diffraction (XRD) and Mössbauer spectroscopy studies. The proposed process is realized by anodic iron polarization in deaerated LiCl solutions containing both water and ethanol. Water seems to play an important role in the synthesis. Morphology of the product was studied by means of transmission electron microscopy and XRD. In the solution containing almost 100% of water a black suspension of round shaped maghemite nanoparticles of 20–40 nm size is obtained. Regulating water concentration allows to control nanoparticle size, which is reduced to 4–6 nm for 5% of water with a possibility to reach intermediate sizes. For 3% or lower water concentration nanoparticles are of a needle-like shape and form a reddish suspension. In this case phase determination is problematic due to a small particle size with the thickness of roughly 3 nm. However, XRD studies indicate the presence of ferrihydrite. Coercivities of the materials are similar to those reported for nanoparticle magnetite powders, whereas the saturation magnetization values are considerably smaller.