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961.
Quirico E Rouzaud JN Bonal L Montagnac G 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(10):2368-2377
The present study questions the sensitivity and the accuracy of Raman spectroscopy as a tool for determining the maturity of natural organic matter (NOM). It focuses on the definition of optimized experimental parameters in order to maximize the quality of the Raman signal and control the accuracy and reproducibility of measurements. A series of 11 coals has been investigated, sampling a wide maturity range (2-7% vitrinite reflectance VR). The role of experimental parameters is first investigated. An excitation wavelength of 514.5 nm gives better results than 457.9 and 632.8 nm, minimizing the fluorescence background observed in the spectra of low-rank coals. Both Raman and fluorescence spectra were investigated with time-resolved experiments in air and argon. These data show that fluorescence and Raman spectra are sensitive to acquisition time and laser power parameters, and reveal a physicochemical instability of the samples under laser irradiation, mostly due to photo-oxidation processes. These data clearly show that the experiments, especially in air, should be performed with strictly constant acquisition parameters. In addition, the results of a whole series of coal measurements performed in air under constant experimental conditions show that Raman spectroscopy is definitely sensitive to the maturity of coal samples with VR> approximately 1%. The most sensitive spectral maturity tracers are the width of the D-band (FWHM-D), the ratio of the peak intensities of the D- and G-bands (I(D)/I(G)), the normalized ratio of the band integrated intensities A(D)/[A(D)+A(G)] for the maturity range VR=3-7% and the width of the G-band (FWHM-G) for VR=1-5%. However, the accuracy and reproducibility are definitely weaker in such measurements compared to the standard VR. Future work must solve the problem of sample stability under laser irradiation, and greatly increase the number of samples to improve the statistical significance of the results. 相似文献
962.
Eric R. Scerri 《Foundations of Chemistry》2005,7(3):327-329
Contents of Volume
Contents of Volume 7 相似文献963.
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967.
Eric Mortenson 《Proceedings of the American Mathematical Society》2005,133(2):321-330
We prove general results on supercongruences between values of truncated hypergeometric functions and their character analogs. As a consequence of the main results of this paper, we prove Beukers-type supercongruences for certain weight three newforms.
968.
The hub location problem with single assignment is the problem of locating hubs and assigning the terminal nodes to hubs in order to minimize the cost of hub installation and the cost of routing the traffic in the network. There may also be capacity restrictions on the amount of traffic that can transit by hubs. The aim of this paper is to investigate polyhedral properties of these problems and to develop a branch and cut algorithm based on these results.Acknowledgement The research of the first author was partially supported by the Banque Nationale de Belgique. The research of the second author was supported by France Telecom R&D under contract no. 99 1B 774. Their support is gratefully acknowledged. 相似文献
969.
We consider infinitely convolved Bernoulli measures (or simply Bernoulli convolutions) related to the -numeration. A matrix decomposition of these measures is obtained in the case when is a PV number. We also determine their Gibbs properties for being a multinacci number, which makes the multifractal analysis of the corresponding Bernoulli convolution possible. 相似文献
970.
The last few years have seen a significant increase in publicly available software specifically targeted to the analysis of
extreme values. This reflects the increase in the use of extreme value methodology by the general statistical community. The
software that is available for the analysis of extremes has evolved in essentially independent units, with most forming extensions
of larger software environments. An inevitable consequence is that these units are spread about the statistical landscape.
Scientists seeking to apply extreme value methods must spend considerable time and effort in determining whether the currently
available software can be usefully applied to a given problem. We attempt to simplify this process by reviewing the current
state, and suggest future approaches for software development. These suggestions aim to provide a basis for an initiative
leading to the successful creation and distribution of a flexible and extensible set of tools for extreme value practitioners
and researchers alike. In particular, we propose a collaborative framework for which cooperation between developers is of
fundamental importance.
AMS 2000 Subject Classification Primary—62P99 相似文献