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111.
G. Stringari Ivo Pancheri Frank Möller Osvaldo Failla 《Accreditation and quality assurance》1998,3(3):122-126
Chemical analyses of trace elements are affected by relatively high analytical errors due to the different steps of the laboratory
procedures: samples grinding, mineralisation and instrumental measurements. In the present communication, the influence of
the grinding phase on the global uncertainty of Pb, Cd, Ni and Cr determinations in plant samples by the classical method
of atomic absorption spectrometry/electrothermal atomisation (AAS-ETA) after dry ashing is quantified. Two grinding machines,
a planetary mill with balls and jars of agate versus a stainless steel grinder were compared by analysing leaf samples of
cucumber, strawberry, kiwivines, apple trees and grapevines from agricultural experimental plots under controlled conditions.
Variance components due to the difference between grinding methods and experimental plots were estimated. Further, the simultaneous
effects of the grinding methods on all considered metals have been evaluated by analysis of variance. With the stainless steel
grinder, on average, higher levels of the considered heavy metals were obtained (up to 67% of the mean values). On average,
the increments were similar for metals contained in steel (Ni and Cr) and those not contained (Pb and Cd). The true causes
of these differences need further investigation to determine whether the higher metal detection is due to possible contamination,
to a different grinding quality or to other reasons. Finally, the grinding methods did not seem to affect the combined uncertainty
of the analyses.
Received: 3 November 1997 · Accepted: 29 November 1997 相似文献
112.
A capillary gas chromatographic method is described for the quantitative determination of liquid paraffin in blood. Paraffin is extracted from blood into n-heptane. After solvent evaporation and dissolution of the residue in 100–200 μl n-heptane one μl is injected into a gas chromatograph fitted with a fused silica capillary column (Permabond® OV-1-CB-0.1, 10 m × 0.32 mm i.d.) and flame ionization detector. Analysis is performed by using an oven program [50°C (3 min)?285°C (5 min), rise 10%min]. The sensitivity (1.5 ng hexadecane) and the reproducibility prove the applicability of the method for the determination of liquid paraffin in blood and for the study of the stability of the liquid paraffin hollow fiber membranes used in an extracorporeal liver support system. 相似文献
113.
S. Küppers 《Accreditation and quality assurance》1997,2(1):30-35
Any analytical data is used to provide information about a sample. The "possible error" of the measurement can be of extreme
importance in order to have complete information. The measurement uncertainty concept is a way to achieve quantitative information
about this "possible error" using an estimation procedure. On the basis of the analytical result, the chemist makes a decision
on the next step of the development process. If the uncertainty is unknown, the information is not complete; therefore this
decision might be impossible. The major problem for the in-process control (IPC) procedure is that not only the repeatability
but also the intermediate precision (which expresses the variations within laboratories related to different days, different
analysts, different equipment, etc.) has to be good enough to make a decision. Unfortunately, the statistical information
achieved from one single analytical run only gives information about the repeatability. This paper shows that the estimation
of the measurement uncertainty for IPC is a way to solve the problem and gives the necessary information about the quality
of the procedure. An example demonstrates that an estimate of uncertainty based on the standard deviations of an analytical
method gives a value similar to one based on the standard deviations obtained from a control chart. Therefore, the estimation
is both a very useful and also a very cost-effective tool. Though measurement uncertainty cannot replace validation in general,
it is a viable alternative to validation for all methods that will never be used routinely.
Received: 24 May 1996 Accepted: 10 August 1996 相似文献
114.
玻璃载体表面脱氧核糖核酸的固定及其化学发光检测 总被引:2,自引:0,他引:2
用硅烷化偶联剂把DNA直接共价固定在载玻片表面,将辣根过氧化物酶标记的探针与之进行核酸杂交,杂交后用增强的化学发光检测。方法的检出限为75pg。研究了DNA分子固定在玻璃载体表面的各种条件,并建立了在玻璃载体表面进行核酸杂交的体系,为研究光纤DNA生物传感器打下了基础。 相似文献
115.
STUDY ON 1-HEXENE POLYMERIZATION BASED ON ZIEGLER-NATTA CATALYSTS WITH DOPED SUPPORT 总被引:1,自引:0,他引:1
XueJiang Zhi-qiangFan 《高分子科学》2004,(4):305-308
A series of Ti/Mg supported catalysts are prepared by using ball-milled mixtures of MgCl2-ethanol adducts and NaCl as supports, and 1-hexene polymerizations catalyzed by the novel catalysts are studied. It is found that the molecular weight distribution of poly(1-hexene) becomes apparently narrower when catalysts with doped supports are used, indicating that changing the structure of the support is an effective way to regulate the active center distribution of heterogeneous Ziegler-Natta catalyst. 相似文献
116.
Yoichi M.A Yamada 《Tetrahedron》2004,60(18):4097-4105
The efficient heterogeneous Heck reaction was achieved by a new networked and supramolecular catalyst PdAS-V (1b). Employing of PdAS-V in 5.0×10−5 mol equiv. efficiently progressed the heterogeneous Heck reaction of a series of aryl iodides with acrylates, styrenes and acrylic acid. PdAS-V was successfully recycled five times without any decrease in its activity, and showed good stability in toluene and water, and hence the Heck reaction was efficiently performed in both reaction media. The use of 8.0×10−7 mol equiv. of PdAS-V resulted in the coupling product in 92% yield with the turnover number (TON) and the turnover frequency (TOF) of PdAS-V reached up to 1,150,000 and 12,000, respectively. The efficient synthesis of resveratrol was achieved via the PdAS-V-promoted Heck reaction. 相似文献
117.
118.
Extrapolated Smoothing Descent Algorithm for Constrained Nonconvex and Nonsmooth Composite Problems*
In this paper, the authors propose a novel smoothing descent type algorithm with extrapolation for solving a class of constrained nonsmooth and nonconvex problems,where the nonconvex term is possibly nonsmooth. Their algorithm adopts the proximal gradient algorithm with extrapolation and a safe-guarding policy to minimize the smoothed objective function for better practical and theoretical performance. Moreover, the algorithm uses a easily checking rule to update the smoothing parameter to ensure that any accumulation point of the generated sequence is an (affine-scaled) Clarke stationary point of the original nonsmooth and nonconvex problem. Their experimental results indicate the effectiveness of the proposed algorithm. 相似文献
119.
120.
民参军是军民融合的重要组成内容,政府支持对于民参军的顺利进行发挥着关键作用。本文通过建立军民融合背景下的地方政府支持与民企参军行为的演化博弈模型,考察了参与者的决策演化过程,分析了参与者的进化稳定策略及影响因素。研究表明,增加地方政府对民企的资金奖励、加大民企参军税收优惠、民企资金收益率的提升,以及积极参军成本的降低,会使民企策略选择向积极参军方向演化,但却使地方政府行为向弱力度支持策略演化;而提升中央政府对地方政府的资金补助,降低地方政府支持民企积极参军的服务成本,不仅促使民企选择积极参军策略,还能促使地方政府选择强力度支持策略。最后,对模型结果进行算例分析,验证了结论的合理性。研究结果可以为当前民参军实践提供一定的理论指导。 相似文献