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151.
P. de Bièvre Robert Kaarls H. Steffen Peiser Stanley D. Rasberry William P. Reed 《Accreditation and quality assurance》1997,2(4):168-179
The authors propose definitions and terminology for protocols on traceability links, generally to the international system
of units, for specific chemical-analytical measurements in accordance with recognized principles of science. These definitions
and terms could be useful in science, technology, commerce or law. A chain of such links leads from a measurand in a sample
up to a unit in the International System of Units or, if unavailable, to a value on an internationally recognized measurement
scale. The quality of such a chain is quantified by combining all recognized uncertainties estimated for all its links. These
uncertainties of the measured values arise from many potential error sources. The protocols should give details of specific
uses of reference materials, measuring instruments and standard measurement methods.
Received: 12 January 1997 Accepted: 31 January 1997 相似文献
152.
In this paper, we introduce a class of graphs that generalize threshold graphs by introducing threshold tolerances. Several characterizations of these graphs are presented, one of which leads to a polynomial-time recognition algorithm. It is also shown that the complements of these graphs contain interval graphs and threshold graphs, and are contained in the subclass of chordal graphs called strongly chordal graphs, and in the class of interval tolerance graphs. 相似文献
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159.
Paul De Bièvre Robert Kaarls H. Steffen Peiser Stanley D. Rasberry William P. Reed 《Accreditation and quality assurance》1996,1(1):3-13
By the definition of the mole as a base unit for amount-of-substance measures within the International System of Units (SI),
chemists can make chemical measurements in full compliance with established metrological principles. Since the mole requires
exact knowledge of the chemical entity, which is often neither available nor of practical relevance to the purpose of the
measurement, the SI units of mass or length (for volume) are unavoidable in the expression of results of many chemical measurements.
Science, technology, and trade depend upon a huge and ever increasing number and variety of chemical determinations to quantify
material composition and quality. Thus, international harmonization in the assessments of processes, procedures, and results
is highly desirable and clearly cost effective. The authors, with relevant experience and responsibilities in Europe and America,
have found some consensus in the interpretation of the metrological principles for chemical measurements, but believe open
discussion should precede wide implementation by chemical communities. In fostering this dialogue, this paper shows, for instance,
that more precise interpretation of the definitions for "traceability," "calibration," and "validation" is needed for present-day
chemical measurements. Problems that face scientists in making measurements do not all vanish just by adherence to the SI.
However, such compliance can improve communication among chemists and metrologists.
Received: 30 June 1995 Accepted: 30 June 1995 相似文献
160.
Krzysztof E. Krakowiak Garren E. Maas Jerald S. Bradshaw Jon K. Hathaway Reed M. Izatt 《Journal of heterocyclic chemistry》1995,32(1):179-181
4,10-Diaza-15-crown-5, 4,10-diaza-18-crown-6, 4,13-diaza-21-crown-7, and 4,16-diaza-24-crown-8 were prepared by an improved method from the appropriate oligothylene glycol diiodides and diamines. The thermodynamic values of log K, ΔH and ΔS for the interaction of 4,10-diaza-18-crown-6 with Pb2+ and Ag+ were determined by a calorimetric titration method and compared with thermodynamic values for interactions of 4,13-diaza-18-crown-6 with the same cations. The thermodynamic values were found to be different for the two diaza-crown ligands. 4,10-Diaza-18-crown-6 and its 4,13-diaza-crown analog formed precipitates when treated with Co2+, Cd2+, Cu2+, and Ni2+ so that no thermodynamic data are reported for these interactions. 相似文献