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
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
When isolating 1,4-dideoxy-1,4-imino-D-arabinitol using Dowex 1(2 (OH- form) or CM-Sephadex C-25 (NH4+ form), we found another compound always accompanied with it. It was apparent that the two compounds had similar structures from their 1HNMR and 13CNMR in D2O (Fig. 1). At first, we guessed the two compounds were isomerides. But when acid was added into the solution of the two compounds, the signals for the minor compound disappeared.Figure 1 13CNMR of 1,4-dideoxy-1,4-imino-D-arabin… 相似文献
A selective and validated stability-indicating LC method was developed for the kinetic study of the degradation of PAC-1, which was carried out in aqueous solutions at 37, 60, 80 and 100 °C with pH 1.5–9.0. Separation was performed on a Kromasil C18 column with acetonitrile–water–fomic acid (30:70:0.1, v/v/v) as mobile phase with a flow rate of 1.0 mL min−1 at 281 nm. The degradation rate obtained indicated a first-order reaction law and the activation energy (Ea) was calculated. The results showed that temperature and pH values were significant factors affecting the degradation of PAC-1. An unknown degradation product in alkaline condition was isolated using a reverse-phase semi-preparative LC system. The structure of the degradation product is identified as 2-hydroxy-3-(2-propenyl)-[[2-hydroxy-3-(2-propenyl)phenyl]methylene]hydrazone utilizing the 1H NMR, 13C NMR, IR and Q-TOF-MS techniques.
Some block iterative methods for solving variational inequalities with nonlinear operators are proposed. Monotone convergence of the algorithms is obtained. Some comparison theorems are also established. Compared with the research work in given by Pao in 1995 for nonlinear equations and research work in given by Zeng and Zhou in 2002 for elliptic variational inequalities, the algorithms proposed in this paper are independent of the boundedness of the derivatives of the nonlinear operator. 相似文献
In this paper, general conditions of state classification for the total weighted occupation times of a class of infinitely
divisible superprocesses on a bounded domain D in ℝd are given. As an application, some sufficient and necessary conditions are found for the total weighted occupation times
of some special superprocesses on D to be absolutely continuous or singular with respect to the Lebesgue measure on D.
The research of Yan-Xia Ren is supported by NNSF of China (Grant No. 10471003) and Foundation for Authors Awarded Excellent
Ph.D. Dissertation. 相似文献