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11.
T. A. Berger 《Journal of separation science》1989,12(2):96-100
A model for restrictor flow produces accurate predictions of flow that can be used to optimize restrictor design. The relative amplitudes of restrictor and other flows and their effect on efficiency are discussed. 相似文献
12.
《Electroanalysis》2005,17(3):255-262
Characteristics of mass transport and potential distribution applicable to microfluidic electrochemical flow cell devices has been modelled using the finite element method. A flexible, automatic grid generation algorithm has been combined with an a‐posteriori error indication technique presented by Nann and Heinze to allow irregular cell geometries to be modelled. The code has been applied to the problem of steady state generator – detector linear sweep voltammetry in a channel flow cell showing the effects of IR drop on the voltammetric response of each electrode. 相似文献
13.
F. Berthelin F. Bouchut 《Annales de l'Institut Henri Poincaré (C) Analyse Non Linéaire》2003,20(6):189-997
We consider isentropic gas dynamics equations with unilateral constraint on the density and mass loss. The γ and pressureless pressure laws are considered. We propose an entropy weak formulation of the system that incorporates the constraint and Lagrange multiplier, for which we prove weak stability and existence of solutions. The nonzero pressure model is approximated by a kinetic BGK relaxation model, while the pressureless model is approximated by a sticky-blocks dynamics with mass loss. 相似文献
14.
Seventeen 1-aryl-2,2-dichlorocyclopropanes were examined by using IR, 13C NMR, and mass spectrometry. The data obtained from IR and 13C NMR spectra indicate that the bond strength of carbon-chlorine on the cyclopropane ring and the electron density of that carbon depend on the substituent. The mass fragmentation patterns of compounds in this series resemble those of the dibromo analogues. The fragmentation mechanism is proposed to involve the formation of indenium ion through an electrocyclization. 相似文献
15.
Moshe Kress 《Annals of Operations Research》2006,148(1):5-23
Handling bioterror events that involve contagious agents is a major concern for authorities and a cause for debate among policymakers
about the best response policy. At the core of this debate stands the question which of the two post-event policies to adopt:
mass vaccination or trace (also called ring or targeted) vaccination. We present a new dynamic epidemic-intervention model that captures key features of the situation and generalizes
some previous assumptions regarding the probability distributions of inter-temporal parameters. It is shown that a mixture
of mass and trace vaccination policies—the prioritized vaccination policy—is more effective than either of the two aforementioned policies. 相似文献
16.
S. Pedersen-Bjergaard T. N. Asp J. Vedde G. E. Carlberg T. Greibrokk 《Chromatographia》1993,35(3-4):193-198
Summary Three chlorinated dimethyl sulfones and five chlorinated thiophenes have been identified in the alkaline extraction liquor from a bleach plant by gas chromatography with atomic emission detection (GC-AED) and with mass spectrometry (GC-MS). The information on elemental content obtained by GC-AED enabled a rapid screening of the sulfur compounds and provided important structural information complementary to the mass spectral data. Quantitation was accomplished by GC-AED based on universal calibration. 相似文献
17.
血液净化用吸附剂脱附过程的数学模型研究 总被引:1,自引:0,他引:1
对已吸附了低密度脂蛋白(LDL)及极低密度脂蛋白(VLDL)达到饱和程度的吸附柱,用1mol/L的生理盐水进行脱附,采用修正Langmuir吸附式建立了连续脱附过程的数学模型,计算结果与实验测定值吻合,表明该数学模型适用于描述类似于LDL及VLDL这类蛋白质大分子的脱附过程。 相似文献
18.
The precision of isotopic measurements of Pb by thermal ionization mass spectrometry (TIMS) is limited by the fact that this element does not possess an invariant isotope ratio that can be used for the correction of mass fractionation by internal normalization. Multiple-collector inductively coupled plasma mass spectrometry (MC-ICPMS) can overcome this limitation, because with plasma ionization, elements with overlapping mass ranges are thought to display identical mass discrimination. With respect to Pb, this can be exploited by the addition of Tl to the sample solutions; the mass discrimination factor obtained for Tl can then be used for the correction of the measured Pb isotope ratios. In this article we present the results of a detailed study that investigates the accuracy and precision of such an external correction technique for mass discrimination based upon the results of multiple analyses of a mixed standard solution of NIST SRM-981 Pb and SRM-997 Tl. Our data indicate that normalization of the Pb isotope ratios to the certified isotopic composition of SRM-997 Tl produces Pb isotopic results that are significantly lower than recently published reference values by TIMS. This systematic offset can be eliminated by renormalization of the Pb data to a different Tl isotopic composition to obtain an empirically determined mass discrimination factor for Pb that generates accurate results. It is furthermore shown that a linear law is least suited for the correction of mass discrimination, whereas a power or exponential law function provide significantly more accurate and precise results. In detail, it appears that a power law may provide the most appropriate correction procedure, because the corrected Pb isotope ratios display less residual correlations with mass discrimination compared to the exponentially corrected data. Using an exponential or power law correction our results, obtained over a period of over seven months, display a precision (2σ) of better than 60 parts per million (ppm) for 208Pb/206Pb and 207Pb/206Pb and of better than 350 ppm for 206Pb/204Pb, 207Pb/204Pb/204Pb, and 208Pb/204Pb. This represents a significant improvement compared to conventional TIMS techniques and demonstrates the potential of MC-ICPMS for routine, high-precision measurements of Pb isotopic compositions. 相似文献
19.
Jürgen Grotemeyer Edward W. Schlag 《Angewandte Chemie (International ed. in English)》1988,27(4):447-459
Mass spectrometry is one of the most important analytical tools in chemistry, biology, medicine and related areas. During the past 30 years, methods have been developed, both for the qualitative as well as the quantitative analysis of a wide variety of substances. The introduction of lasers into chemistry has also profited mass spectrometry, since its nonlinear properties and its tunability open up fundamentally new frontiers. Multiphoton ionization mass spectrometry combines UV-spectroscopy and mass spectrometry, thus providing a two-dimensional method that enables substance-specific and even state-specific analyses. This progress report presents the fundamentals and possibilities of MUPI mass spectrometry and discusses investigations on amino acids, peptides, chlorophylls and sugars. For each substance, multiphoton ionization can be tuned in such a way that only the molecular ion is formed. An increase of laser intensity induces substance-specific fragmentations of the molecule, thus contributing to a quick and easy identification of the substance. 相似文献
20.
R. Hoelzl Christian Hoelzl Ludwig Kotz Lazlo Fabry 《Accreditation and quality assurance》1998,3(5):185-188
Inductively coupled plasma mass spectrometry (ICP-MS) and high resolution inductively coupled plasma mass spectrometry (HR-ICP-MS)
are powerful methods of determining metallic impurities in the low- and sub-ppt level in process media such as ultra-pure
water used in semiconductor and wafer manufacturing. By using mass spectrometers for analysis, an isotope dilution analysis
(IDMS) is possible. The reproducibility of an IDMS is unmatched. For concentration levels near the instrument detection limit
a novel method is reported to find the optimal amount of isotopic spike solution. This optimal value can be derived by the
law of propagation of uncertainty combined with the Poisson statistics of the measured number of counts. Generally, an excess
of isotopic spike solution should be used to provide results of lowest possible uncertainty. The results are presented in
a diagram for easy practical use.
Received: 14 October 1997 · Accepted: 13 February 1998 相似文献