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71.
The condensation of 1,5-diaminoimidazoles with ethyl aceto-acetate gives two types of compounds: imidazo[1,5-b]-1,2,4-triazepinones and imidazo[4,5-b]pyridinones. The structure of these compounds is demonstrated by rmn and mass spectroscopy. The formation of imidazo[4,5-b]pyridinones from imidazo[1,5-b]-triazepinones through a new transposition is also shown. 相似文献
72.
Ph. Quevauviller 《Journal of chromatography. A》1996,750(1-2):25-33
The awareness of a need for an improved control of environmental contamination levels has led to the development of new hyphenated techniques for the determination of a wide variety of chemical species (e.g., organotins, methyl-mercury, alkyl-lead compounds etc.). These techniques generally involve many analytical steps such as extraction, derivatisation, separation and detection which have to be carried out in such a way that the speciation is not changed during the abalytical process. The need for evaluating the method's performance has led the BCR programme of the European Commission (now Standards, Measurements and Testing programme) to conduct series of interlaboratory studies during the last decade. These projects followed a step-by-step approach for the evaluation of different steps of the analytical methods used, e.g., simple solutions to test the detection, cleaned extract to evaluate the separation, spiked samples to test the extraction and natural samples to evaluate the whole analytical procedures. These collaborative projects allowed most of the sources of errors related to either a technique or a laboratory to be detected and removed. This paper gives an account of discussions of possible errors occurring in speciation analysis and presents examples of technical scrutiny of hyphenated techniques using chromatography as applied to the determination of tributyltin, methyl-mercury and trimethyllead. 相似文献
73.
Philippe Quevauviller Gemma Rauret Allan Ure Roser Rubio José-Fírmin López-Sánchez Haidé Fiedler Herbert Muntau 《Mikrochimica acta》1995,120(1-4):289-300
The determination of extractable trace metal contents in soil using single extraction procedures is currently performed in many laboratories to assess the bioavailable metal fraction (and related phytotoxic effects) and the accessability to the environment (e.g. contamination of ground waters). Owing to the need for validation of the extraction schemes used and of the analytical techniques, the EC Measurements and Testing Programme (formerly BCR) has organized a project for improving the quality of determination of extractable trace metal contents in soil, the first step being an interlaboratory study to adopt common extraction procedures and the second being a certification campaign to certify two soils for their extractable trace element contents following these procedures. This paper gives a brief overview of the project organisation and describes the preparation, homogeneity and stability studies of two soil candidate reference materials (sewage sludge-amended and terra rossa soils). 相似文献
74.
T. A. Armstrong M. Benayoun I. J. Bloodworth J. N. Carney C. J. Dodenhoff C. Evangelista B. R. French B. Ghidini M. Girone A. Jacholkowski J. Kahane J. B. Kinson A. Kirk K. Knudson V. Lenti Ph. Leruste A. Malamant J. L. Narjoux F. Navach A. Palano N. Redaelli L. Rossi M. Sené R. Sené M. Stassinaki G. Vassiliadis O. Villalobos Baillie M. F. Votruba G. Zito 《Zeitschrift fur Physik C Particles and Fields》1992,56(1):29-36
We have studied the reactions \(({{\pi ^ + } \mathord{\left/ {\vphantom {{\pi ^ + } p}} \right. \kern-0em} p})p \to ({{\pi ^ + } \mathord{\left/ {\vphantom {{\pi ^ + } p}} \right. \kern-0em} p})(K\bar K\pi )p\) where the \(K\bar K\pi \) system is centrally produced, at 85 GeV/c and 300 GeV/c using the CERN Omega spectrometer. A spin-parity analysis of theK S 0 K ± π ? system shows the presence of a strongJ PC=1++ signal which we identify as theE/f 1 (1420) meson. We also find evidence for the decayE/f 1(1420)→K S 0 K S 0 π 0 which determines theC-parity of this state to be positive. Alternative explanations of the data have been tested and ruled out. Hence we obtain the quantum numbers of theE/f 1 (1420) to beI G(JPC)=0+(1+). 相似文献
75.
We study Schrödinger operators of the form
on
d
, whereA
2 is a strictly positive symmetricd×d matrix andV(x) is a continuous real function which is the Fourier transform of a bounded measure. If
n
are the eigenvalues ofH we show that the theta function
is explicitly expressible in terms of infinite dimensional oscillatory integrals (Feynman path integrals) over the Hilbert space of closed trajectories. We use these explicit expressions to give the asymptotic behaviour of (t) for smallh in terms of classical periodic orbits, thus obtaining a trace formula for the Schrödinger operators. This then yields an asymptotic expansion of the spectrum ofH in terms of the periodic orbits of the corresponding classical mechanical system. These results extend to the physical case the recent work on Poisson and trace formulae for compact manifolds.Partially supported by the USP-Mathematisierung, University of Bielefeld (Forschungsprojekt Unendlich dimensionale Analysis) 相似文献
76.
The investigations performed in this work have demonstrated that an easy-axis frustrated non-Heisenberg magnet can contain homogeneous phases with the vector (ferromagnetic) and tensor (nematic) orderings, as well as a spatially inhomogeneous phase of the magnetic spiral type. Depending on the relationships between the material parameters, either a ferromagnetic spiral or a spiral of the quadrupole–ferromagnetic type with different periods of the spiral structures can be formed in the system. The phase diagram of the system has been constructed. 相似文献
77.
The aim of this study is the evaluation by mechanical testing of the durability of rigid PVC. The prediction of mechanical durability is made by following the change in the brittle temperature TB at a constant speed by an indentation test after artificial and natural weathering. TB is presented as a possible durability index for thin, extruded rigid PVC profiles. 相似文献
78.
A study by convergent beam electron diffraction has been performed in order to clarify the symmetry of the phase III of Pb2CoWO6. Microdiffractions with higher-order Laue zone on monodomain areas have confirmed the cell proposed in our preceding study. In addition, an ‘axial’ glide plane (c) has been found normal to the b axis. In the conditions of observation, the convergent beam electron diffraction patterns lead to an apparent point group mmm. No breakdown of a mirror symmetry could be found. The discrepancy between this result and the existence of a spontaneous polarisation is discussed. 相似文献
79.
80.
Ph. Savignac E. Elia Aboujaoude N. Collignon M. P. Teulade 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-2):491-494
Abstract Phosphoryl and silyl chlorides phosphonoalkylation lead to the direct generation of phosphonyl-phosphonyl and phosphonyl-silyl carbanions the properties of which are discussed. 相似文献