Study of jump models for the diffusion of hydrogen in NbH0.02 by means of the quasielastic scattering of slow neutrons

The quasielastic scattering of slow neutrons in a NbH_0.02 single crystal has been measured for a wavevector transfer Q between 0.5 ≤ |Q| ≤ 2.5 Å^?1 at 293, 431 and 581 K for several sample orientations. The data have been analysed in terms of several jump models for the diffusion of hydrogen by comparing the spectral lineshape with the incoherent scattering law S_inc(Q, ω) of the models. The model of jumps to nearest-neighbor sites becomes progressively worse with increasing temperature. The discrepancy cannot be remedied by taking into account jumps to the second-neighbor sites. On the other hand the measured spectral lineshape can be well reproduced in the whole |Q| range by a double-jump model and a two-state model. For comparison, the method of fitting one Lorentzian to theory and experiment has also been used.     

Investigation of the optic modes in VH0.51 by neutron spectroscopy

We have measured the frequencies of the optic modes of VH_0.51 at different temperatures in the α-, β- and ε -phases. In the β -phase a new mode was detected at 220 meV. The threefold splitting in the ε-phase is consistent with an off center location of Hydrogen. The frequencies are well reproduced by a force constant model with an axially symmetric metal Hydrogen interaction.     

Incoherent structure factor of hydrogen in NbH0.11

We show that the measurement of the quasielastic energy spectrumS(Q,) of incoherently scattered neutrons provides a direct andprecise method to determine the location of the H atom diffusing on interstitial sites in a metal lattice. At the reciprocal lattice points the spectrum contains a sharp elastic line with a relative intensity which is equal to the structure factor of the occupied sites. In a neutron scattering experiment performed on a NbH_0.11 single crystal, we have measured the structure factor at the (110), (200) and (222) reflection at elevated temperatures (148°C and 280°C). Our results give clear evidence of tetrahedral site occupancy and exclude an appreciable partial occupation of octahedral (3%) and triangular sites (7%) at 280°C. These findings support the basic assumption of the Chudley Elliott theory in the study of jump diffusion models of H assuming a negligible flight time in the jump process between neighbouring sites.     

Banach manifold structure and infinite-dimensional analysis for causal fermion systems

Annals of Global Analysis and Geometry - A mathematical framework is developed for the analysis of causal fermion systems in the infinite-dimensional setting. It is shown that the regular spacetime...     

The Debye-Waller factor and the diffusion process for hydrogen in Nb,Ta, and V single crystals investigated by neutron spectroscopy

Quasielastic scattering of slow neutrons on hydrogen diffusing in the-phase of NbH_0.02, TaH_0.13 and VH_0.07 single crystals was investigated in a wide range of temperatures and scattering vectorsQ (0.5Q2.5 Å^–1). The incoherent scattering lawS _d (Q,) for four different diffusion models was consistently compared with the measured lineshapes. At elevated temperatures one had to introduce correlated jumps to describe the experimental data, whereas at room temperature a model with jumps between adjacent sites is sufficient. The integrated quasielastic intensityI(Q) obtained from the fit ofS _d (Q,) with the measured spectra follows an isotropic Debye-Waller factor with mean square amplitudes u ²=0.02–0.04 Ų for H in Ta (20°C–500°C), and u ²=0.03–0.04 Ų for H in Nb (20°C–300°C). For H in V,I(Q) obtained from the analysis of the quasielastic scattering deviates from a normal Debye-Waller factor behaviour. This effect is assumed to be due to the flight process between the interstitial sites. On the other hand, a normal Debye-Waller factor was obtained from theQ-dependence of the inelastic scattering of the band modes, with values of u ²=0.02–0.04 Ų (135°C–500°C). The observed values of u ² were compared with theoretical calculations.     

A systematic comparison of four different workup procedures for systematic toxicological analysis of urine samples using gas chromatography–mass spectrometry

Sample preparation for systematic toxicological screening analysis (STA) in urine by gas chromatography–mass spectrometry (GC-MS) generally involves cleavage of conjugates by acid hydrolysis (Hy) or enzymatic hydrolysis (Gluc) followed by liquid–liquid extraction (LLE) or solid-phase extraction (SPE), and derivatization, e.g., acetylation (Ac). LLE and derivatization can be performed simultaneously, e.g., in extractive methylation (ExMe). The work presented consisted of two separate studies. In study I, 350 urine samples from 168 inpatients from an internal medicine ward were worked up by Hy-LLE-Ac, the standard workup in the authors’ laboratory, Gluc-SPE-Ac, and Gluc-ExMe. In study II, 100 urine samples from psychiatric inpatients were worked up by Hy-LLE-Ac and Hy-SPE-Ac. The samples prepared were analyzed by full-scan GC-MS, and the drugs and/or their metabolites/artifacts detected after the different workup procedures were compared. The results obtained after Hy-LLE-Ac and Gluc-SPE-Ac showed only little differences, e.g., salicylic acid not being detectable with the latter. Hy-SPE-Ac covered a similar range of analytes as Hy-LLE-Ac but was much more time-consuming. Comparison of Hy-LLE-Ac and Gluc-ExMe showed that the former was better suited for basic drugs and the latter for acidic drugs, but the overlap was considerable. In conclusion, Hy-LLE-Ac remains the method of choice for STA in clinical toxicology owing to its wide analyte spectrum and short workup time. Gluc-ExMe is an ideal complementary method when acidics need to be covered. Gluc-SPE-Ac can be used as an alternative to Hy-LLE-Ac when turnaround is not critical or when automated analysis is required. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Some of these results were reported at the 46th International TIAFT Meeting, Martinique, 2–8 June 2008.