正确使用分析天平

使用分析天平时,在什么情况下,需要重新校正天平的零点? 1.称量次数过多,中间最好校正几次零点。不要一直称量下去,否则最后产生疑点就晚了,有些样品发生变化,会造成失败。 2.几个人连续使用天平,每换一个人时,应当校正一次天平的零点。 3.称量中间间隔时间过长,重新使用时应校正一次天平的零点。 4.称量变化大的样品。如吸附性和挥发性强,或过于干燥和过于湿的样品,称量中要多校正几次天平的零点。 5.称量中不慎将样品从皿中洒落秤盘上,取下秤盘擦拭后,必须重新校正天平空秤的零点。 6.称量中不慎碰撞过天平的某个部件或整体时,应当重新调…     

我国工程起重机行业的现状及发展

文章是对我国工程起重机行业的不理想的企皿效率现状进行了分析。随着我国建设和谐社会，追求持续协调发餍的提出，我国传统行业发展的效率问题日益凸显．文章提出随着解决我国工程起重机行业的效率问题的外部条件日趋成熟。     

膨胀合金与热双金属

500458热双金属的热处理一(BaoHHH I(J. A.)《CTa二砂,1980,灿1,SU一时(俄文)500459双金属管样品的机械性能测定一一 (Ma卫‘。A.月.)《3aao双。.皿a6.》, 1979,恤12,1137一1138(俄文)500460爆炸焊接热双金属板的最佳热处理制度 -一(Ko刀。班班e双E .M.)《CTa刀。》,1980, 纯1,62一63(俄文)膨胀合金与热双金属~~     

Discussing Problems of Chinese Interest Rate liberalization

eo。。c loball。tlon hashas een卜…a pod edof world econonuc developthent since the rond WOrld Wr呵以ally 1980’s nd it has en alle(3tln econOIny,IX)ll－ties,cdtllle皿d 1血 s阿ieJevery comp In山e wo洲bveq dee．In。ent y。the tlend of lobaiZationfix)ves forwald,Wllltih acceleyaes the frs tr3tle and ationaldistribution Of natulal rer,llroes,merehantuse,capital,thehnolop皿d 讪Mm山on。a咖bl。de．5ely cmp,叫驷m。dd。efope or血vebping countn。,卜枯卜把nb皿砂 into lobal ec。c netWO上。如…     

标准样品证书和标签的内容要求

1.引言在介绍标准样品证书和标签内容要求之前,首先应该区别两个问题:一是有证标准样品(CRM)证书和一般标准样品(RM、QCM)证书在性质上的差异;二是证书和证书内容要求的差异。对于第一个问题,在我国,有证标准样品的含义是经过有关标准化主管部门批准、发布的标准样品,根据《中华人民共和国标准化实施条例》第十一条和第十三条的规定:我国只有两种有证标准样品,它们分别为国家标准样品(目前由国家标准化管理委员会批准发布)和行业标准样品(由各个行业标准化主管部门批准发布)。也就是说:有证标准样品的生产(包括研制和复制)必须获得国家…     

北京市消协公布定量包装商品计量体验调查报告

正9月6日,北京市消费者协会公布了定量包装商品计量体验调查报告。报告显示,两成多样品存在缺斤短两问题。其中,胶带样品不够长的问题最多,垃圾袋样品数量缩水位居第二,湿巾样品和保鲜袋样品数量不足位居第三。只有抽纸样品的实际净含量全部达到或超过标注净含量要求,占比达到100%。据委托调查方北京阳光消费大数据技术研究院介绍,本次体验调查选取了49种、5大类     

地质样品的化学分析与样品的保存

地质样品在地质科学研究中具有非常重要的作用,是地质资源相关研究、生态学研究与环保领域重要研究对象。伴随科技进步,地质样品的分析技术也获得了较大的改进和发展,而对于样品的保存的问题也引起越来越多的关注,如何做好样品保存,防止样品不必要的损耗甚至影响分析结果是业内学者所关心的重要问题。我国目前在这一方面尚有诸多欠缺,本文针对于此进行分析、讨论并给出建议,以期提供思路与参考。     

也谈光度比色分析中皿间误差的修正

也谈光度比色分析中皿间误差的修正胡勇（贵州清镇中国第七砂轮厂计测处，５５１４１４）在《计量技术》１９９３年第８期３０页，刊登了题为“光度比色分析中皿间误差的扣除”的文章（以下简称“扣除”）。笔者对其进行了仔细的阅读，结合自己的研究体会，提出了一些不同...     

上海市声学学会历届理事会组成成员

第一届理事会 ( 1980年 1983年)由魏墨今酉皿、冯绍松、李宝善、叶奕坤、王季卿、朱西、周永昌、郑冠雄、梁之安、王务同、王鸿樟、向大威、余衍甲、张本厚、张泽琦、赵松龄、赵振良、赵乐山、赵梓光、闻恽、施乃平、徐之江、徐智章、黄杏宝、章奎生、谢世栋、管玉书等 2 7位同志组成。魏墨今酉皿同志任理事长 ;冯绍松、李宝善同志任副理事长 ;叶奕坤同志任秘书长 ;1982年增补蒋济良同志任副秘书长 ;王季卿、朱西、周永昌、郑冠雄、梁之安等 5位同志为常务理事。第二届理事会( 1983年 1986年)由魏墨今酉皿、冯绍松、李宝善、黄杏宝、王务同…     

液体样品预处理装置中黏稠液体定量转移结构创新

为解决液体样品预处理装置中罐体之间黏稠液体定量转移无法准确实现的问题,综合应用发明问题解决理论(TRIZ)和约束理论(TOC)进行问题分析与求解。从系统的角度分析了样品预处理装置的组成及要素间的相互关系,基于TRIZ进化模式和TOC必备树确定了样品预处理装置的核心问题,应用基于TRIZ的计算机辅助创新软件InventionTool 3.0中的冲突模块、标准解模块和效应模块进行了设计方案的选择、评价和修正,提出了实现液体样品预处理装置中黏稠液体定量转移的原理解。     

Laser-glazing low carbon iron fracture samples

Charpy samples of low carbon steel were laser-glazed in the V-notch root, resulting in highly modified fracture properties and radially altered crystal structure. Laser-glazing produced two distinct regions: (a) an inner region, next to the bulk material, which was heated above the austenitic transition temperature, was cooled rapidly, and produced a retained austenitic phase, and (b) an outer region, next to the V-notch surface, which was heated above the melting temperature, cooled more slowly, although still very rapidly, and transformed predominantly into the martensite phase. Instrumented impact testing of laser-glazed samples produced fracture energies and fracture toughness values similar to samples prepared by currently accepted ASTM precracking procedures. Laser-glazing is offered as an alternative to existing procedures as an experimental technique for testing fracture toughness samples and, especially, for testing substandard size samples and hard-to-prepare, fracture toughness materials samples.     

Impurity Effect on Wear Resistance of Ultrafine-Grained Copper

The wear properties of ultrafine-grained(UFG) Cu samples of different purities were investigated in comparison with the coarse-grained(CG) Cu.The UFG Cu samples,prepared by means of plastic deformation via quasistatic compression,exhibit an enhanced wear resistance relative to the CG Cu samples.For both the UFG and the CG Cu samples,wear volumes increase at higher purities.A steady state worn subsurface structure was formed in each sample after sliding for 60 min,consisting of a heavily deformed nanostructured mixing layer(NML) on top of a continuous dynamic recrystallization(DRX) layer.A pronounced correlation is identified that wear volume increases monotonically with an increasing grain size of the DRX layer.The impurity level of the Cu samples has an obvious influence on the DRX grain sizes,which in turn determines the wear resistance of the Cu samples.     

基于在线半监督学习的故障诊断方法研究

针对机械故障诊断中准确、完备的故障训练样本获取困难,而现有分类方法难以有效地发掘大量未标记故障样本中蕴含的有用信息,提出了一种基于在线半监督学习的故障诊断方法.该方法基于Tri-training算法将在线贯序极限学习机从监督学习模式扩展到半监督学习模式,利用少量不精确的标记样本构建初始分类器,并从大量未标记样本中在线扩充标记样本,对分类器进行增量式更新以提高其泛化性能.半监督基准数据试验结果表明,训练样本总数相同但标记样本数与未标记样本数比例不同时,所提算法得到的分类准确率相当且训练时间相差小于1.2倍.以柴油机8种工况的故障模式为对象进行试验验证,结果表明标记故障样本较少时,未标记故障样本的加入可使故障分类准确率提高5％～8％.     

The magnetic properties of nanocrystalline CoLa0.1Fe1.9O4 ferrite under an external AC magnetic field

CoLa_0.1Fe_1.9O₄ ferrite nanocrystal was synthesized under an induced AC magnetic field by the emulsion method. From XRD pattern, it is shown that all the samples are cubic structure of the spinel ferrite. The morphology of samples synthesized under an induced AC magnetic field was flake-like in shape from TEM image. Both the strength and acting time of external magnetic field influence the crystallite sizes of samples. Magnetic properties of samples were measured by vibrating samples magnetometer (VSM). The changing morphology of sample when an external magnetic field was applied, which might be responsible for the low magnetic properties.     

Influence of microstructure and hydrogen concentration on amorphous silicon crystallization

Hydrogenated amorphous silicon samples were deposited on glass substrates at different temperatures by high frequency plasma-enhanced chemical vapor deposition. In this way, samples with different hydrogen concentrations and structures were obtained. The transition from an amorphous to a crystalline material, induced by a four-step thermal annealing sequence, has been followed. Effusion of hydrogen from the films plays an important role in the nucleation and growth mechanisms of crystalline silicon grains. Measurements of hydrogen concentrations, Raman scattering, X-ray diffraction and UV reflectance showed that an enhanced crystallization was obtained on samples deposited at lower substrate temperatures. A correlation between these measurements allows to analyze the evolution of structural properties of the samples. The presence of voids in the material, related to disorder in the amorphous matrix, results in a better quality of the resulting nanocrystalline silicon thin films.     

Comparative study of the nonlinear behavior of fatigued and intact samples of metallic alloys

A method and an experimental setup to study the nonlinear behavior of fatigued and intact metal samples under high-frequency stresses has been developed and tested. The method is based on the measurement of the vibration velocity of stepped bar samples flexurally and/or extensionally vibrating at resonance. The vibration velocity signal, picked up by a laser vibrometer, is automatically acquired and analyzed by classical fast Fourier transform (FFT) methods for different excitation levels. The experimental setup was designed in such a way that it can be used for fatiguing and for testing the material samples. The tests have been done with samples of titanium and aluminium alloys. Results before and after fatigue crack nucleation are compared. A strongly nonlinear, nonclassical behavior is observed for fatigued samples. Theoretical interpretations of the different nonlinear behavior of standing waves in fatigued and intact samples are explored, and the results of the models are qualitatively compared with the experimental data. The models' approach provides an interpretation about the origin of nonlinearity in fatigued samples.     

Magnetic stability of SnO₂ nanosheets

Room temperature ferromagnetism has been observed in freshly synthesized and post-annealed SnO? nanosheets. The results of x-ray diffraction and x-ray photoelectron spectroscopy reveal that the newly synthesized samples and those annealed at 400?°C under either an O? or Ar atmosphere possess rutile structure and no other impurity phases are observed. The fitting results of the O 1s and Sn 3d spectra from SnO? samples annealed at 400?°C under an O? or Ar atmosphere both indicate that oxygen vacancies inevitably exist in these samples. It is found that the saturation magnetization of all the annealed samples does not feature mono-dependence on oxygen vacancies, whereas an Sn vacancy related origin seems more plausible to account for variations in the magnetization of samples studied. This finding corresponds to first-principle calculation results from our previous work. Furthermore, the Curie temperature of SnO? nanosheets was estimated to be around 300?°C, rendering it a very good option for the next generation of spintronics.     

Influence of hydrogen on the current density of Nb3Sn multifilamentary conductors

The overall current density of Nb3Sn multifilamentary conductors heat-treated with hydrogen and argon is quite different. At flux densities above 11 T hydrogen samples carry more current than argon samples. below 11 T argon samples are superior to hydrogen samples. The transition temperature of hydrogen samples is generally found to be some tenths of a Kelvin below that one of the argon samples. X-ray investigations at room temperature indicate an increase of the lattice spacing in hydrogen samples corresponding to a growth of the unity cell up to 0.6% . The critical current of hydrogen samples undergoing tensile stress will increase in a way similar to argon samples.     

Continuous segmented-flow polymerase chain reaction for high-throughput miniaturized DNA amplification

A continuous segmented-flow method for sequential DNA amplification is described in order to provide a basis for high-throughput genetic analysis. The approach allows an immediate distinction between amplified and nonamplified products. A mixture of sample and reagents are loaded in the form of small segments one after another in a 15-m-long narrow-bore Teflon tube, coiled such as to be repeatedly exposed to three different temperature zones. After having passed the heated zones, the samples are mixed with an intercalating dye by flow injection and sequentially detected on-line by laser-induced fluorescence. The aqueous samples travel as separate segments in a continuous flow of an immiscible, organic liquid. Perfluorodecalin was shown to be particularly suitable due to its hydrophobicity and inert properties. To reduce carryover between samples, an intermediate water plug between two consecutive samples was required. Selected regions from human genomic DNA were successfully amplified in 300-nL volumes after 30 passes through the heated zones. The total reaction time was approximately 45 min, and the detection interval between individual samples was 1 min. Automation and the possibility to further reduce sample volumes, as well as to employ many reaction columns simultaneously, should provide a platform for an extremely high throughput.