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11.
Mendels P Bert F de Vries MA Olariu A Harrison A Duc F Trombe JC Lord JS Amato A Baines C 《Physical review letters》2007,98(7):077204
We report muon spin rotation measurements on the S=1/2 (Cu2+) paratacamite ZnxCu4-x(OH)6Cl2 family. Despite a Weiss temperature of approximately -300 K, the x=1 compound is found to have no transition to a magnetic frozen state down to 50 mK as theoretically expected for the kagomé Heisenberg antiferromagnet. We find that the limit between a dynamical and a partly frozen ground state occurs around x=0.5. For x=1, we discuss the relevance to a singlet picture. 相似文献
12.
Using chiral probes shown to be sensitive to the presence of mobile phase additives, a memory effect for these additives by an amylosic column was demonstrated. Exposure to these additives gave prolonged chromatographic performance changes even after their removal from the mobile phase. This finding is consistent with strong binding of the additives to the stationary phase. A procedure to remove bound additives was developed. 相似文献
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Evolution of solid-phase microextraction technology 总被引:18,自引:0,他引:18
The main objective of this contribution is to describe the development of the concepts, techniques and devices associated with solid-phase microextraction, as a response to the evolution of understanding of the fundamental principles behind this technique. The discussion begins with an historical perspective on the very early work conduced almost a decade ago. As new fundamental understanding about the functioning of the technology developed, new ways of constructing and using the SPME devices evolved. 相似文献
14.
We consider the analytic continuation of the commutator[q
m, pn for values of m,n positive integers. This is carried out both in the Moyal algebra and the operator algebra. 相似文献
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van Enk SJ 《Physical review letters》2000,84(4):789; author reply 790
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Francesco De Matteis Gwyn A. Lord 《Rapid communications in mass spectrometry : RCM》2008,22(24):4055-4065
We have used open‐chain tetrapyrroles, such as bilirubin, as molecular probes to investigate the pro‐oxidant activity of desferrioxamine (DES) and its modulation by Trolox. On exposure to Fe‐EDTA/H2O2, bilirubin and mesobilirubin underwent bleaching. When DES was present, bleaching was prevented and both rubins were converted into green‐coloured derivatives and then into red pigments. Trolox added with DES inhibited the colour changes induced by DES. The oxidative products were resolved from their parent compounds by high‐performance liquid chromatography (HPLC) and studied by electrospray ionization mass spectrometry and by UV/visible spectroscopy. The green products were identified as biliverdin or mesobiliverdin; the red pigments as the 1:1 molar adduct of DES with biliverdin or mesobiliverdin, less two hydrogens in both cases. It is concluded that DES exercises its oxidative activity through nitroxyl oxidizing radicals capable of efficient hydrogen abstraction, dehydrogenating either rubin to the corresponding verdin. A diradical derivative of DES (bearing two nitroxyl radicals in the same molecule) may be involved in the oxidation of verdins to red pigments, through concerted dehydrogenation and adduct formation. These results shed further light on the redox properties of bilirubin, DES and Trolox, and their interactions. They provide further evidence of the pro‐oxidant activity of DES and suggest a more general biological significance, as rapid removal of bilirubin by bleaching or dehydrogenation may have pharmacological/toxicological implications in severe jaundice. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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This paper explores the use of pulsed radio-frequency (RF) techniques to remove the frequency limitations imposed on conventional transverse muon spin rotation (μSR) experiments at a pulsed muon source by the finite muon pulse width. The implementation of the 90° pulse technique is demonstrated by observing the free precession signal of diamagnetic muons implanted in polythene, the change in signal amplitude as a function of RF pulse length is plotted and the precise condition for a 90° pulse determined. The technique is evaluated by comparing measurements made using conventional spin rotation experiments to those employing pulsed RF methods. The potential for applying standard NMR multiple-pulse methods to the μSR experiment is considered and the use of two-pulse RF sequences (90° x ?τ?90° x and 90° x ?τ?180° x ) to form a muon spin echo demonstrated. 相似文献