共查询到20条相似文献,搜索用时 125 毫秒
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研制了无氧水标准物质,配制成水溶液测量其溶解氧浓度,并进行均匀性和稳定性验证,对测定值结果的不确定度进行了评定。结果表明,该无氧水标准物质具有良好的均匀性,在12个月内溶解氧浓度没有显著性变化,稳定性良好,溶解氧测定值结果的扩展不确定度为0.05 mg/L (k=2)。该标准物质可用于溶解氧测定仪的零点误差项目的测定。 相似文献
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依据GB 5274-2008《气体分析校准用混合气体的制备称量法》对氮中氢、氮中氧、氮中硫化氢标准气体的配制、定值及其不确定度进行了分析和阐述,讨论了影响测量不确定度的主要来源,该过程和方法可用于其他标准气体的配制和不确定度分析. 相似文献
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以氮中二氧化碳二级气体标准物质的研制为例,探讨采用比较法研制二级气体标准物质及其不确定度的分析计算,其中标准物质的制备采用称量法配制,并对所研制的样品进行了均匀性、稳定性试验,结果表明,所研制的氮中二氧化碳气体的标准物质在一年的考察期内,其均匀性、稳定性、量值不确定度均达到国家二级标准物质要求,符合申报条件。 相似文献
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In 1985, the CODATA Bulletin published a Report of its Task Group on Thermophysical Properties of Solids which analyzed available
data on, and gave recommended values for, the heat capacity of Cu, Fe, W, and Al2O3, the thermal expansion of Cu, Si, W, and Al2O3, the electrical resistivity of Cu, Fe, Pt, and W, the thermal conductivity of Al, Cu, Fe, and W, and the absolute thermopower
of Pb, Cu, Pt, and W. The analysts for the different properties were R. B. Castanet, S. J. Collocott, P. D. Desai, C. Y. Ho,
J. G. Hust, R. B. Roberts, C. A. Swenson, and G. K. White. The present paper is an updated version of the earlier report and
includes more recent data which change some of the recommended values. notably the heat capacity of Cu and W and the thermal
expansion of Si and W. 相似文献
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Enjun Song Yuhe Chen Anbang Li Yuxiang Sun Rui Yang Jing Wang 《Materials and Manufacturing Processes》2017,32(12):1428-1434
In this paper, using furfural residue as a template, porous calcium titanate (FPCT) was prepared by a sol-gel method and characterized by XRD, SEM, and nitrogen adsorption method. The conditions of preparation were investigated. The adsorption capabilities of FPCT for heavy metal ions were studied, and the adsorption mechanism was investigated. The results show that the calcium titanate was porous, and material is composed of crystals in nanoparticle size with a small amount of calcium sulfate impurities, while the sulfuric acid in furfural residue is fixed as the calcium sulfate in the material. The adsorbed quantity is affected by the pH value of medium and time. When the pH value of medium is 5, and oscillating adsorption lasts for 30?min, the adsorbed quantities of Cd, Pb, Zn, Cu, and Ni are 118.04, 197.96, 64.98, 56.85, and 47.91?mg/g, respectively. The adsorption conforms to the Langmuir adsorption isothermal model and pseudo-second-order kinetic equation, and is a spontaneous endothermic process driven by entropy. After adsorption, adsorbents can be regenerated with 1?mol/L nitrate solution. It is used for eliminating Cd, Pb, Zn, Cu, and Ni in wastewater and the results are satisfactory. 相似文献
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制备了负载1%白藜芦醇(Res)的三种脂质纳米载体,分别为固体脂质纳米粒(SLN)、纳米脂质载体(NLC)和纳米乳(NE),通过进行离心、粒径、zeta电位、pH值、含量、包封率及对温度的稳定性等理化性质研究,结果表明,Res-SLN,粒径45±5nm,zeta电位-10.0±0.3mV,含量为9.57mg.mL-1,包封率为98.68%;Res-NLC,粒径185±3nm,zeta电位-10.8±0.5mV,含量为9.17mg.mL-1,包封率为99.36%;Res-NE,粒径7nm,zeta电位-4.8±0.4mV,含量为9.89mg.mL-1,包封率为97.97%。三种载体体系在4℃及25℃离心10000r/min,30min不分层。分别在室温、4℃、40℃下放置15d,Res-NLC表现出良好的稳定性。 相似文献
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The data produced by high-throughput genomic techniques are often high dimensional and undersampled. In these settings, statistical
analyses that require the inversion of covariance matrices, such as those pursuing supervised dimension reduction or the assessment
of interdependence structures, are problematic. In this article we show how the idea of adding noise to the bootstrap, pioneered
by Efron, and Silverman and Young, in the late seventies and eighties, can be used to overcome undersampling and effectively
estimate the inverse covariance matrix for data sets in which the number of observations is small relative to the number of
variables. We demonstrate the performance of this approach, which we call augmented bootstrap, on simulated data and on data derived from genomic DNA sequences and microarray experiments.
This invited paper is discussed in the comments available at: , , , , , , , .
This work was partially supported by NIH grant HG02238 to W. Miller, NIH grant R01-GM072264 to K. Makova, and NSF grant DMS-0704621
to R.D. Cook, B. Li and F. Chiaromonte. 相似文献
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This research explores the injury severity of pedestrians in motor-vehicle crashes. It is hypothesized that the variance of unobserved pedestrian characteristics increases with age. In response, a heteroskedastic generalized extreme value model is used. The analysis links explanatory factors with four injury outcomes: fatal, incapacitating, non-incapacitating, and possible or no injury. Police-reported crash data between 1997 and 2000 from North Carolina, USA, are used. The results show that pedestrian age induces heteroskedasticity which affects the probability of fatal injury. The effect grows more pronounced with increasing age past 65. The heteroskedastic model provides a better fit than the multinomial logit model. Notable factors increasing the probability of fatal pedestrian injury: increasing pedestrian age, male driver, intoxicated driver (2.7 times greater probability of fatality), traffic sign, commercial area, darkness with or without streetlights (2-4 times greater probability of fatality), sport-utility vehicle, truck, freeway, two-way divided roadway, speeding-involved, off roadway, motorist turning or backing, both driver and pedestrian at fault, and pedestrian only at fault. Conversely, the probability of a fatal injury decreased: with increasing driver age, during the PM traffic peak, with traffic signal control, in inclement weather, on a curved roadway, at a crosswalk, and when walking along roadway. 相似文献
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David R. Smith F. R. Fickett 《Journal of research of the National Institute of Standards and Technology》1995,100(2):119-171
Pure silver is used extensively in the preparation of high-temperature superconductor wires, tapes, films, and other configurations in which the silver not only shields the superconducting material from the surrounding materials, but also provides a degree of flexibility and strain relief, as well as stabilization and low-resistance electrical contact. Silver is relatively expensive, but at this stage of superconductor development, its unique combination of properties seems to offer the only reasonable means of achieving usable lengths of conductor. In this role, the low-temperature physical (electrical, thermal, magnetic, optical) and mechanical properties of the silver all become important. Here we present a collection of properties data extracted from the cryogenic literature and, to the extent possible, selected for reliability. 相似文献
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J. H. Hubbell 《Journal of research of the National Institute of Standards and Technology》1990,95(6):689-699
Photon and particle radiations (gamma rays, x rays, brems-strahlung, electrons and other charged particles, and neutrons) from radioactive isotopes, x-ray tubes, and accelerators are now widely used in gauging, production control, and other monitoring and metrology devices where avoidance of mechanical contact is desirable. The general principles of radiation gauges, which rely on detection of radiation transmitted by the sample, or on detection of scattered or other secondary radiations produced in the sample, are discussed. Examples of such devices currently used or at least shown to be feasible in industrial, transportation, building, mining, agricultural, medical, and other metrology situations are presented, drawing from a total of 146 selected technical and review paper reference sources here cited. 相似文献
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Imagineering is a portmanteau combining the words imagination and engineering. The term, imagineering, was coined during the early 1940s. Since the new Millennium, imagineering has grown to the scale of a mass paradigm, because of the increasing scope and availability of automated engineering. Automated engineering is enabled by sophisticated software and artificial intelligence (AI) across the virtual-social-physical convergence (VSP) of consumer devices, desktop machines, and Web platforms. The combining of human imagination with automated engineering is enabling millions of vloggers, self-publishers and makers to imagineer at high speed and low cost. This mass imagineering can range from early education to digital afterlife. It involves makerspaces, fab labs, hackerspaces, as well as use of disparate devices, machines, and platforms “in the wild”. In this paper, three principal contributions to the literature are provided. First, mass imagineering is described from early education to digital afterlife. Second, analysis of structure and agency in mass imagineering is provided. This reveals that individual agency varies in different settings for mass imagineering, but is always more than in mass production and mass customization settings. Third, division of labour analysis of mass imagineering is provided. This reveals that mass imagineering extends labour outside of paid employment, such as in the home, towards greater self-expression and increased entrepreneurship. This is possible because of increasing automated engineering across VSP enabled by devices, machines, and platforms. 相似文献
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Satnam Singh Dheeraj Gupta Vivek Jain Apurbba K. Sharma 《Materials and Manufacturing Processes》2015,30(1):1-29
The main focused aim of developing new processing and manufacturing technologies are to reduce production or manufacturing costs, processing times, and to enhance manufactured product properties. The developed processing techniques should be widely acceptable for all types of materials including metal matrix composites, ceramics, alloys, and fiber reinforced plastics. Microwave materials processing is emerging as a novel processing technology which is applicable to a wide variety of materials system including processing of MMC, FRP, alloys, ceramics, metals, powder metallurgy, material joining, coatings, and claddings. In comparison to the conventional processes, microwave processing of materials offers better mechanical properties with reduced defects and economical advantages in terms of power and time savings. The present review work focuses mainly on global developments taking place in the field of microwave processing of materials and their relevant industrial applications. 相似文献