排序方式: 共有40条查询结果,搜索用时 265 毫秒
21.
22.
23.
Dayse Luzia Pinheiro da Silva Yahya Mrestani Hans-Hermann Rüttinger Johannes Wohlrab Reinhard Neubert 《Chromatographia》2008,67(9-10):813-817
Simple methods for the quantification of taurine by capillary electrophoresis are described. Qualitative and quantitative comparisons between fluorescence detection after precolumn derivatization and direct detection by integrated pulse amperometry were performed. A calibration curve was constructed with standard taurine solutions and confirmed by standard addition to representative sample solutions. Fluorescence detection gave superior sensitivity (LOD, 7.5 × 10?6 μmol L?1). There was no significant difference in taurine values (p > 0.001) observed by either method of detection. 相似文献
24.
25.
26.
Dynamic clustering for interval data based on L
2 distance 总被引:2,自引:0,他引:2
Francisco de A. T. de Carvalho Paula Brito Hans-Hermann Bock 《Computational Statistics》2006,21(2):231-250
Summary This paper introduces a partitioning clustering method for objects described by interval data. It follows the dynamic clustering
approach and uses and L
2 distance. Particular emphasis is put on the standardization problem where we propose and investigate three standardization
techniques for interval-type variables. Moreover, various tools for cluster interpretation are presented and illustrated by
simulated and real-case data. 相似文献
27.
28.
D. Hupfeld W. Schweika J. Strempfer W.A. Caliebe U. Köbler K. Mattenberger G.J. McIntyre F. Yakhou Th. Brückel 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(3):273-289
We report on an investigation of the magnetic properties of Gd
x
Eu
1 - x
S mixed crystals with compositions in the range of 0.6 <
x
< 1. For the two samples Gd
0.8
Eu
0.2
S and Gd
0.73
Eu
0.27
S a long-range antiferromagnetic order was observed at low temperatures. Element-specific measurements exhibited a different
temperature dependence of the reduced sublattice magnetisation of the two magnetic species. A model calculation and Monte
Carlo simulations revealed that the different temperature dependence is due to frustration effects. These frustration effects
lead to a breakdown of the long-range order for higher europium contents. For the Gd
0.67
Eu
0.33
S-sample we were able to observe a short-range antiferromagnetic order with correlation lengths of a few 10? with X-ray resonance exchange scattering.
Received 25 April 2001 and Received in final form 3 December 2001 相似文献
29.
Badea SL Vogt C Gehre M Fischer A Danet AF Richnow HH 《Rapid communications in mass spectrometry : RCM》2011,25(10):1363-1372
α-Hexachlorocyclohexane (α-HCH) is the only chiral isomer of the eight 1,2,3,4,5,6-HCHs and we have developed an enantiomer-specific stable carbon isotope analysis (ESIA) method for the evaluation of its fate in the environment. The carbon isotope ratios of the α-HCH enantiomers were determined for a commercially available α-HCH sample using a gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) system equipped with a chiral column. The GC-C-IRMS measurements revealed δ-values of -32.5 ± 0.8‰ and -32.3 ± 0.5‰ for (-) α-HCH and (+) α-HCH, respectively. The isotope ratio of bulk α-HCH was estimated to be -32.4 ± 0.6‰ which was in accordance with the δ-values obtained by GC-C-IRMS (-32.7 ± 0.2‰) and elemental analyzer-isotope ratio mass spectrometry (EA-IRMS) of the bulk α-HCH (-32.1 ± 0.1‰). The similarity of the isotope ratio measurements of bulk α-HCH by EA-IRMS and GC-C-IRMS indicates the accuracy of the chiral GC-C-IRMS method. The linearity of the α-HCH ESIA method shows that carbon isotope ratios can be obtained for a signal size above 100 mV. The ESIA measurements exhibited standard deviations (2σ) that were mostly < ± 0.5‰. In order to test the chiral GC-C-IRMS method, the isotope compositions of individual enantiomers in biodegradation experiments of α-HCH with Clostridium pasteurianum and samples from a contaminated field site were determined. The isotopic compositions of the α-HCH enantiomers show a range of enantiomeric and isotope patterns, suggesting that enantiomeric and isotope fractionation can serve as an indicator for biodegradation and source characterization of α-HCH in the environment. 相似文献
30.
F Buchner HH Ritze M Beutler T Schultz IV Hertel A Lübcke 《The Journal of chemical physics》2012,137(2):024503
Time-resolved liquid jet photoelectron spectroscopy was used to explore the excited state dynamics at the liquid water surface in the presence of alkali cations. The data were evaluated with the help of ab initio calculations on alkali-water clusters and an extension of these results on the basis of the dielectric continuum model: 160 nm, sub-20 fs vacuum ultraviolet pulses excite water molecules in the solvent shell of Na(+) or K(+) cations and evolve into a transient hydrated complex of alkali-ion and electron. The vertical ionization energy of this transient is about 2.5 eV, significantly smaller than that of the solvated electron. 相似文献