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931.
A diffusive sampling method for the determination of low-molecular isocyanates as their 4-nitro-7-piperazinobenzo-2-oxa-1,3-diazole (NBDPZ) derivatives using tandem mass spectrometry (MS/MS) after atmospheric pressure chemical ionisation (APCI) is presented. Isocyanic acid (ICA), methyl isocyanate (MIC), ethyl isocyanate (EIC) and phenyl isocyanate (PhIC) are collected on NBDPZ-impregnated polystyrene divinyl benzene (SDB) filter tapes. The method was validated for MIC, EIC and PhIC for concentrations between 0.5 and 50 ppb at relative humidity (RH) conditions from 10 up to 90%. Validation was carried out by active sampling using 1-(2-methoxyphenyl)piperazine (2-MP) as derivatising agent. Sampling periods applied were between 15 min and more than 8 h. The sampling rates were determined to be 21.0 mL/min for MIC with a relative standard deviation (RSD) of 9.0% for 184 samplers, 15.6 mL/min for EIC (RSD 11.6%; N = 154) and 11.5 mL/min for PhIC (RSD 8.4%; N = 87). The limits of quantification were 1.4 ppb for MIC and 1.3 ppb for EIC and PhIC applying 15 min sampling periods. Owing to high background signals, isocyanic acid could only be determined when it was present in concentrations in the high ppb range. 相似文献
932.
A new alpha-methylanthraquinone glucoside, laccaic acid D 8-o-beta-D-glucoside, and six known anthraquinones have been isolated from the aqueous alcoholic extract of Emex spinosus (L.) Campd. (Polygonaceae), together with two known flavonol glycosides. The structures were determined by conventional analytical methods and confirmed by MS and NMR spectral analysis, including 2D experiments for the new compound. 相似文献
933.
The lithium double diphosphates LiCryFe1−yP2O7 have been investigated by X-ray diffraction, SQUID measurements and vibrational spectroscopy. The Rietveld refinements based on the XRD patterns show the existence of a continuous solid solution over the whole composition range (0?y?1.0) with a continuous evolution of the monoclinic unit cell parameters (S.G. P21). The transition metal ions connect the diphosphate anions forming a three-dimensional network with channels filled by Li+ cations expected to exhibit high mobility. All compounds order magnetically at low temperatures due the Fe-Fe interactions. The ordering temperature decreases with increasing Cr content. The slope in Curie-Weiss fits to the 1/χ vs T data in the paramagnetic domain clearly shows the existence of Fe3+ and Cr3+ in their high spin states, and a ferromagnetic component is clearly detected for y=0, 0.2 and 0.4. IR spectra have been interpreted using factor group analysis. The small shift of the frequencies is due to the influence of the chromium amount. The POP angles were estimated using the Lazarev's relationship. 相似文献
934.
Bond angles at thiohydroxamate oxygen in crystal structures of 3-alkoxy-5-(p-methoxyphenyl)-4-methylthiazole-2(3H)-thiones gradually increased with the size of the 3-alkoxy substituent. This effect was attributed to strain on the basis of (i) a linear free energy relationship (Taft-Dubois correlation) and (ii) signal coalescence from resonances of diastereotopic CH3 groups in solution (O-cumyl substituent; DNMR). Substitution at oxygen along the sequence OR (R=prim-, sec-, and tert-alkyl), OH, and OLi was reflected in a gradual decrease of N,O distances and lengthening of associated C,S bonds. The responsivity for these changes was more pronounced in the thiazole-2(3H)-thione than in the pyridine-2(1H)-thione series. 相似文献
935.
Cedrik Meier Stephan Lüttjohann Vasyl G. Kravets Hermann Nienhaus Axel Lorke Hartmut Wiggers 《Physica E: Low-dimensional Systems and Nanostructures》2006,32(1-2):155
The Raman spectra of silicon nanoparticles in the size range between d=3.5– have been studied experimentally. Scattering processes up to second order are being observed. The experimental results are analyzed in the framework of the phonon confinement model. While this model describes qualitatively the observations for first-order scattering processes, it is not applicable for scattering processes of higher order. From the analysis of second-order scattering, we determine a redshift of the TO phonon at the X and L points. 相似文献
936.
937.
The nonlinear dynamic behavior of a simple system with an elastohydrodynamic line contact is investigated. The elastohydrodynamic problem is solved with finite differences including streamline upwind techniques. The results are stored in a lookup table for an effective calculation of the frequency response. It is found that the system exhibits rich nonlinear dynamic behavior including jump phenomena as well as sub- and superharmonic bifurcations. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
938.
Hartmut Hetzler 《PAMM》2009,9(1):275-276
Within this contribution, the general form of perturbation equations for systems of moving elastic bodies is derived and examined with respect to symmetry and definiteness properties. The contact is enforced by a penalty formulation, which is motivated by a constitutive contact model relying on statistical data of the surface. Evaluating Hamilton's Principle and carrying out a linearization about a stationary transport motion, the general perturbation equations are derived. The resulting differential operators are stated and discussed. The findings are exemplified for a rotating cicular Timoshenko beam with frictional contacts. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
939.
Minimally doubled fermions have been proposed as a cost-effective realization of chiral symmetry at non-zero lattice spacing. Using lattice perturbation theory at one loop, we study their renormalization properties. Specifically, we investigate the consequences of the breaking of hyper-cubic symmetry, which is a typical feature of this class of fermionic discretizations. Our results for the quark self-energy indicate that the four-momentum undergoes a renormalization which is linearly divergent. We also compute renormalization factors for quark bilinears, construct the conserved vector and axial-vector currents and verify that at one loop the renormalization factors of the latter are equal to one. 相似文献
940.