Fragmentation of plumeran indole alkaloids from Aspidosperma spruceanum by electrospray ionization tandem mass spectrometry

The fragmentation of six plumeran indole alkaloids (PIAs) previously isolated from Aspidosperma spruceanum has been investigated by electrospray ionization tandem mass spectrometry (ESI‐MS/MS) in the positive ion mode. The fragmentation pathways have been established on the basis of MS/MS experiments using fragment ions generated in‐source and deuterium‐labeled alkaloids as precursor ions and on the basis of accurate mass measurements. Our results demonstrated that the fragmentation routes observed for the protonated PIAs are essentially derived from a pericyclic reaction and from the opening of rings D and E, followed by 1,4‐hydrogen rearrangements. Product ions resulting from radical eliminations were also observed, contrary to the ‘even‐electron rule’. Our data reveals that some product ions from protonated PIAs provide crucial information for the characterization of the acyl substituent at N‐1, the methoxyl and hydroxyl groups at the aromatic moiety, and give evidence of an ether bridge between C‐18 and C‐21. The data reported here were used for the dereplication of these compounds in a stem bark methanolic extract of Aspidosperma spruceanum. Copyright © 2010 John Wiley & Sons, Ltd.     

Über positive Fourier-Integrale

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Hydrogen adsorption on Gd(0001)

The electronic structure of hydrogen adsorbate-induced states on Gd(0001) was investigated by means of photoelectron spectroscopy with linearly polarized radiation. The E vector of the incoming photon beam is rotatable. Clean and well-ordered rare-earth (0001) surfaces exhibit a highly localized surface state near the Fermi edge. After the adsorption of hydrogen, the surface state disappears and an additional sharp feature at about 4 eV binding energy is observed. For this latter state, the ratio of the radial matrix elements as well as the relative phase shifts were determined to be R=R_p/R_f=2.4±0.3 and δ_f−δ_p=310±10°, respectively. The removal of the Gd surface state by hydrogen adsorption was investigated by means of scanning tunneling microscopy (STM) and spectroscopy (STS). The removal of the surface state exhibits domain-like behavior, with surface steps acting as domain boundaries. The tunneling spectra reveal that hydrogen adsorption causes a dramatic reduction in the differential conductivity near the Fermi level.     

Coarse-Grid-CFD for the Thermal Hydraulic Investigation of Rod-Bundles

A nuclear reactor core, that is a few meters in height and diameter is composed of hundreds of fuel assemblies which are again composed of tenth of fuel rods with a diameter of about 10 mm. The relevant length scales for a Computational Fluid Dynamics (CFD) simulations range from the sub millimetre range, relevant for the sub channels up to several meters. Describing such a multi-scale situation with CFD is extremely challenging and the traditional approach is to use integral methods. These are sub channel and sub assembly analyses codes requiring closure by empirical and experimental correlations. A CFD simulation of a complete nuclear reactor set up resolving all relevant scales requires exceedingly large computational resources. However, in many cases there exists repetitive geometrical assemblies and flow patterns. Based on this observation the general approach of creating a parametrized model for a single segment and composing many of these reduced models to obtain the entire reactor simulation becomes feasible. With the Coarse-Grid-CFD (CGCFD) ( [1], [2]), we propose to replace the experimental or empirical input with proper CFD data. Application of the methodology starts with a detailed, well-resolved, and verified CFD simulation of a single representative segment. From this simulation we extract in tabular form so-called volumetric forces which upon parametrization is assigned to all coarse cells. Repeating the fine simulation for multiple flow conditions parametrized data can be obtained or interpolated for all occurring conditions to the desired degree of accuracy. Note, that parametrized data is used to close an otherwise strongly under-resolved, coarsely meshed model of a complete reactor set up. Implementation of volumetric forces are the method of choice to account for effects as long as dominant transport is still distinguishable on the coarse mesh. In cases where smaller scale effects become relevant the Anisotrop Porosity Formulation (APF) allows capturing transport phenomena occurring on the same or slightly smaller scale compared to the coarse mesh resolution. Within this work we present results of several fuel assemblies, that were investigated with our methodology. In particular, we show Coarse-Grid-CFD simulations including a 127 pin LBE cooled wire wrapped fuel assembly. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)