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991.
André Haefliger 《Commentarii Mathematici Helvetici》1962,36(1):47-82
Sans résumé
This work was partially supported by NSF Grant G-10.700. 相似文献
992.
The determination of the concentration of light elements, such as carbon, nitrogen and oxygen, in e.g. atmospheric aerosol
particles is important to study the chemical behaviour of atmospheric pollution. The knowledge of low-Z element concentrations gives us information on the speciation of nutrients (species having nutritional value for plants)
and toxic heavy metals in the particles. The capability of the conventional energy-dispersive EPMA is strongly limited for
the analysis of low-Z elements, mainly because the Be window in the EDX detector hinders the detection of characteristic X-rays of light elements
such as C, N, O and Na. WDS is suitable for analysis of light elements, but the measurement of beam sensitive microparticles
requires the minimisation of the beam current and the measurement time. A semi-quantitative analytical method based on EPMA
using an ultra-thin window EDX detector was developed. It was found that the matrix and geometric effects that are important
for low-energy X-rays can be reliably evaluated by Monte Carlo calculations. Therefore, the quantification part of the method
contains reverse Monte Carlo calculation done by iterative simulations. The method was standardised and tested by measurements
on single particles with known chemical compositions. Beam-sensitive particles such as ammonium-sulphate and ammonium-nitrate
were analysed using a liquid nitrogen cooled sample stage. The shape and size of the particles, which are important for the
simulations, were determined using a high-magnification secondary electron image. Individual marine aerosol particles collected
over the North Sea by a nine-stage Berner cascade impactor were analysed using this new method. Preliminary results on five
samples and 4500 particles show that the method can be used to study the modification of sea-salt particles in the troposphere. 相似文献
993.
A. Stephen K. Hashmi Prof. Dr. Christian Lothschütz Dipl.‐Chem. Martin Ackermann Dipl.‐Chem. René Doepp Dipl.‐Chem. Sankaran Anantharaman Benjamin Marchetti Dipl.‐Chem. Helmut Bertagnolli Prof. Dr. Frank Rominger Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(27):8012-8019
Gold complexes were prepared and investigated as catalysts for the oxidative esterification of aldehydes. Stabilisation by pyridine ligands gave good conversions and the in situ extended X‐ray absorption fine structure (EXAFS) study of the reactions indicated that the reaction mixtures contained only mononuclear gold species. Thus, this is the first proof for a homogeneous gold‐catalysed oxidation reaction; the presence of nanoparticles could be excluded experimentally. 相似文献
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998.
This work investigates different hemp surface modifications (mercerization, maleated polyethylene (MAPE) addition in solution or in melt blending) to improve the properties of linear medium density polyethylene (LMDPE). From the composites produced, a complete morphological and tensile characterization was performed for a fixed hemp content (30% wt.). The morphological analysis showed that both the direct (melt blending) and solution modifications were able to significantly improve the composites interface quality and therefore the tensile properties (151% increase in modulus and 36% increase in strength over the neat matrix) within the range of conditions tested. 相似文献
999.
In this paper we give an overview of some aspects of the min-max theory of minimal surfaces, and discuss recent applications to conformally invariant problems in Geometry and Topology. The goal is to explain what the proofs of the Willmore conjecture for surfaces and the Freedman-He-Wang conjecture for links share in common. This is based on joint work of the authors [19] and on joint work of I. Agol and the authors [1]. 相似文献
1000.