751-G分光光度计几种常见故障的检修

751-G型分光光度计可从紫外测量到可见光波段,是应用较广泛的一种化学分析仪器。在检定工作中常遇到以下几种故障情况:一、开机后,暗电流档指示表针不稳定。此情况有以下几种可能,须逐一排除(见图1)1.光电管老损用下述方法对图1中的2个光电管分别进行排查。将光电管转换开关K2置于可见光档(或紫外光档),如表针不稳定,再置于中间位置(751-G型仪器,其开关K2是可以置于中间位置的,此时K2与两个光电管都已断开)。若表针稳定了,表明可见光(或紫外光)的光电管已老化,须更换。2.微电流放大器故障,按以下顺序排查(1)将开关K2置于中间位置,若表针…     

三状态开关式波动率的美式看跌期权

本文研究三状态开关式波动率美式看跌期权的定价问题,假设波动率σ(t)取三个不同的值σ1,σ2,σ3,分别对应于股市中的熊市、振荡市和牛市,利用Δ对冲技巧得到了有三条自由边界(即最佳实施边界)的变分不等式模型;作为其应用,本文得到以下结果:若当前股票市场处于熊市(牛市),则在一定条件下,三状态开关式波动率美式看跌期权的最佳实施边界比标准美式看跌期权的最佳实施边界大(小),且三状态开关式波动率美式看跌期权的价格比标准美式看跌期权的价格低(高);若当前股票市场处于振荡市,则在一定条件下,三状态开关式波动率美式看跌期权的最佳实施边界比标准美式看跌期权的最佳实施边界小(大),且三状态开关式波动率美式看跌期权的价格比标准美式看跌期权的价格高(低)。     

电极温度的测量

在低功率电路中,在开关断开瞬间,因电弧而产生热量,这个热量是使开关腐蚀的原因.开关相当于两个电极.根据电弧电功率与电极接收的热功率之差值,可以估计电极的腐蚀量.电弧电功率的测定与计算,已有文献报道.要计算电极接受的热功率,必须首先测出电极的温度.由于开关(电极)断开时,电弧持续时间极短(约为3—6ms),及对周围产生热扩散等等原因,使得电极温度的测量甚为复杂.本文介绍了电极温度测量的试验装置、方法、结果与应用.     

应用于无线通信的小型化微带缝隙可重构天线

提出了一种新型的小型化频率可重构天线,通过两个开关二极管控制天线的频率,实现频率的重构.天线结构新颖简单,采用宽缝隙天线上加载开关,且开关易于操作控制.当开关闭合时,天线的实测结果谐振频率在5.34 GHz,反射系数为-23.4 dB,相对带宽为70%,实现了超宽带.当开关断开时,天线的实测结果谐振频率为2.4 GHz...     

高压、快速开关GaN功率晶体管的技术途径

本文主要讨论用于功率电子电路中的快速开关GaN器件的技术途径。首先,概述对于在SiC和Si衬底上生长的器件,用于提高击穿电压的最先进技术。然后将这些技术与不同偏压下的动态开关特性联系起来。动态开关特性仍然落后于类似的竞争器件,尤其是如果考虑高偏压的开关特性时。开关特性一般用所谓的动态导通电阻表示。它与一些工艺参数的关系极大,这些参数如外延层的设计、缓冲层晶体品质、钝化层,最后,但并不是不重要的是横向器件设计(如场电极的布置)。说明了所有这些影响因素之间的平衡,及其与GaN高压开关器件现状的关系。     

温敏聚氨酯膜开关温度阀值及其调控途径

合成了三种温敏聚氨酯TSPU(a)、TSPU(b)和TSPU(c),并对其软段相的转变温度(即开关温度)进行了表征,同时研究了不同种类聚氨酯的相容性对共混体系开关温度阀值的影响。DSC分析表明:TSPU(a)、TSPU(b)和TSPU(c)为典型嵌段结构,其开关温度阀值分别为50.6℃,55.7℃和3.5℃。软段相结构相似的TSPU(a)与TSPU(b)的共混物仅具有一个开关温度,其阀值决定于共混体系中两聚合物的相对含量;而软段相结构不同的TSPU(a)与TSPU(c)共混物具有两个独立的开关温度,但其阀值相互靠拢。采用不同熔点和不同有序性的聚醚(酯)二元醇作为软段以及将组成和结构相似或不相似的温敏聚氨酯共混,是调节温敏聚氨酯开关温度阀值的有效途径。     

简单易制的观众厅渐明渐暗照明开关

中国电影业进入了快速发展的时期,电影院的装修档次和服务质量日益提高,给观众厅安装一个渐明渐暗的照明开关,当开始放映时让观众厅的灯光逐渐变暗,放映结束时灯光逐渐变亮,避免灯光从亮到暗或者从暗到亮的跳跃变化给观众的视觉造成不舒适的强烈刺激,让观众厅具备更加人性化的放映氛围。专业的渐明渐暗调节开关不但价格高,除新款放映机和配电柜整体配备外一般不易买到。根据电影院的实际需要,我们自行设计实验制作了一种简易的灯光渐明渐暗控制开关,成本低廉,易于制作,下面作一介绍。线路原理图如下图,由整流、电流调节、延时控制、稳压几部…     

晶体管接近开关在锅炉提煤机上的运用

4 t及以上快装锅炉大多利用卷扬机在滑道上提升提煤机煤斗加煤,煤斗上下运行是通过碰撞上、下行程开关,控制电机正反转来实现.由于行程开关经常易碰坏,而且煤斗停止位置也不十分准确,影响正常生产.针对如此情况,设计用晶体管接近开关代替普通行程开关, 并在线路上加设时间继电器(见图1),整个过程仅需按启动按钮一次完成.     

材料试验机的加载指示装置

在用材料试验机进行压缩试验时,为了控制好加载速度,需要了解试验机是否已施加上载荷,以便迅速调整送油阀的大小,为此我们在改造一台原东德产30t(300kN)材料试验机电气部分时,加装了加载指示灯装置,它能迅速、准确地告知操作者,试验机是否已施加上载荷.根据摆锤式试验机的工作原理,当给试样施加上载荷时,摆杆离开铅垂位置.因此,我们把摆杆作为指示灯亮、熄的控制机构.选一微动开关,用它的一对常闭触点,使它在摆杆离开铅垂位置(试验机刚加上载荷)时,电路处于闭合状态,此时指示灯亮,表明试验机开始施加载荷;当试验机未施加载荷时,摆杆在铅垂位置,开关处于断开状态,指示灯不亮,表明试验机未开始加载.电路原理如图1所示.     

基于压电元件的半主动振动控制的研究

为了克服主/被动控制中存在的缺点,提出了一种基于同步开关阻尼技术的半主动振动控制新方法.基于该方法的控制系统简单,只要一些电子元器件就可以实现振动控制,且控制效果好、鲁棒性高.采用此方法能有效对悬臂复合梁进行了振动控制.由于半主动控制方法的控制效果主要取决于电路品质因子以及开关切换的延时时间,因此通过探讨这两个参数对控制效果的影响,推导了基于开关切换延时的半主动振动控制的阻尼公式,搭建了悬臂复合梁振动半主动实验平台,对理论分析结果进行了实验验证.     

Gender differences in publication productivity in psychology in India

An analysis of gender differences in psychology in India provides quantitative and qualitative assessment of R&D output contributed by psychologists with the indication of the trend of growth, skewness, relatedness, co-authorship pattern of productivity.     

Metrology in Chemistry in Germany

The system for Metrology in Chemistry in Germany is described. At the national standards level, a network of high-level chemistry institutes coordinated by the national metrology institute, PTB, provides the primary references for chemical measurements. A dissemination mechanism employs chemical calibration laboratories accredited within the framework of the German Calibration Service (DKD). They act as “multipliers” between the national standards level and the user level by providing the user with calibration means which are traceable to the SI via national standards. Traceability structures in clinical chemistry, electrochemistry, elemental analysis and gas analysis are described     

Natural radioactivity in drinking water in private wells in Finland

Natural radioactivity in drinking water was determined in population-based random study of 472 private wells. The mean concentrations of (222)Rn, (226)Ra, (234)U, (238)U, (210)Pb and (210)Po in drilled wells were 460, 0.05, 0.35, 0.26, 0.04 and 0.05 Bq l(-1), and in wells dug in the soil were 50, 0.016, 0.02, 0.015, 0.013 and 0.007 Bq l(-1), respectively. Approximately 10% of the drilled wells exceeded a radon concentration of 1000 Bq l(-1) and 18% a uranium concentration of 15 microg l(-1). The mean annual effective dose from natural radionuclides for a drilled well user was 0.4 mSv and 0.05 mSv for a user of a well dug in the soil. The effective dose arising from (222)Rn was 75% of the total of all natural radionuclides for drilled well users. As regards long-lived radionuclides, (210)Po and (210)Pb caused the largest portion of the effective dose. The dose arising from (238)U, (234)U and (226)Ra was only 8% of the total of all natural radionuclides.     

Natural radioactivity in drinking water in private wells in Finland

Radiation Protection Dosimetry     

Optische in situ Schichtdickenmessung in Bedampfungsanlagen. Optical in situ film thickness monitoring in coating systems

Optical film thickness monitoring is more precise than crystal monitoring. The optical measurement makes use of the fact that the intensity of a monochromatic light beam which is reflected on a film will change periodically with increasing film thickness. The measurement is performed at an exchangeable test glass that is positioned beside the substrates and is therefore coated in the same way as the substrates. The accuracy of cut‐off is achieved by a “fit” of a theoretical curve shape to the measured values. Order filters are used to ensure that, at a certain wavelength, higher deflection orders do not influence the measurement when a monochromator grating is used.     

Spanish experience in education and training in radiation protection in medicine

In most of its publications, the International Commission on Radiological Protection has highlighted the importance of education and training in radiation protection (RP) for medical exposures. Spain, like other Member States of the European Union, has implemented the Directive and the Guidelines in the medical area. The purpose of this paper is to present the Spanish experience in RP education and training in medicine, the different objectives established according to professional levels, existing regulations and feedback obtained from various RP actions.     

Differences in coagulation in clotting of vascular access in hemodialysis patients

Arteriovenous graft (AVG) thrombosis is a frequent cause of graft failure. We evaluated coagulation protein concentrations, platelet function, and viscoelasticity factors in 20 hemodialysis (HD) patients with AVGs. The goal was to determine whether significant differences in protein concentrations, platelet function, and viscoelasticity factors exist among dialysis patients requiring frequent AVG declot procedures vs. those who do not. Twenty HD patients were enrolled: 10 frequent clotters (>3 declots in the previous year) and 10 were nonclotters. Patients on antiplatelets or chronic anticoagulation were excluded. Laboratories were drawn pretreatment and heparinase was added to counteract any potential heparin effect. Coagulation protein concentrations including tissue factor (TF), thrombin/antithrombin III complex (TAT), and prothrombin fragment 1 + 2 (F₁₊₂) were assayed. The time to clot onset was measured by force onset time (FOT). Platelet contractile force (PCF) measured the force produced by platelets during clot retraction, whereas clot rigidity was measured as clot elastic modulus (CEM). FOT, CEM, and PCF were measured by Hemodyne. Both groups had upregulation of the TF pathway, as TF, TAT, and F₁₊₂ levels were similarly increased over baseline levels. Hemodialysis patients with frequent AVG clotting had higher levels of both PCF and CEM compared with nonclotters. Additionally, the frequent clotters had a lower FOT relative to nonclotters, although both were considered in the normal range. Our study suggests that HD patients with recurrent AVG thrombotic events form clots with higher tensile strength compared with HD patients without recurrent graft thrombosis.