47 research outputs found
In situ-XAS and catalytic study of acrolein hydrogenation over silver catalyst: Control of intramolecular selectivity by the pressure
The gas phase hydrogenation of acrolein over 7.5% Ag/SiO2 has been studied in a broad pressure range from 7.5 mbar to 20 bar. Higher pressures favour the formation of allyl alcohol (selectivities up to 42%), whereas at low pressures propionaldehyde is by far the main product. In situ-XAS has been performed at 7.5 mbar in order to gain insight into the interaction of acrolein with Ag(1 1 1). Hydrogenated propionaldehyde-like surface species could be detected which orientated parallel to the surface. The observed intermediate correlates perfectly with the online catalytic data
Grazing incidence x ray fluorescence analysis for non destructive determination of In and Ga depth profiles in Cu In,Ga Se2 absorber films
Development of highly efficient thin film solar cells involves band gap engineering by tuning their elemental composition with depth. Here we show that grazing incidence X ray fluorescence GIXRF analysis using monochromatic synchrotron radiation and well characterized instrumentation is suitable for a non destructive and reference free analysis of compositional depth profiles in thin films. Variation of the incidence angle provides quantitative access to the in depth distribution of the elements, which are retrieved from measured fluorescence intensities by modeling parameterized gradients and fitting calculated to measured fluorescence intensities. Our results show that double Ga gradients in Cu In1 x,Gax Se2 can be resolved by GIXR
Mathematical modelling of clostridial acetone-butanol-ethanol fermentation
Clostridial acetone-butanol-ethanol (ABE) fermentation features a remarkable shift in the cellular metabolic activity from acid formation, acidogenesis, to the production of industrial-relevant solvents, solventogensis. In recent decades, mathematical models have been employed to elucidate the complex interlinked regulation and conditions that determine these two distinct metabolic states and govern the transition between them. In this review, we discuss these models with a focus on the mechanisms controlling intra- and extracellular changes between acidogenesis and solventogenesis. In particular, we critically evaluate underlying model assumptions and predictions in the light of current experimental knowledge. Towards this end, we briefly introduce key ideas and assumptions applied in the discussed modelling approaches, but waive a comprehensive mathematical presentation. We distinguish between structural and dynamical models, which will be discussed in their chronological order to illustrate how new biological information facilitates the âevolutionâ of mathematical models. Mathematical models and their analysis have significantly contributed to our knowledge of ABE fermentation and the underlying regulatory network which spans all levels of biological organization. However, the ties between the different levels of cellular regulation are not well understood. Furthermore, contradictory experimental and theoretical results challenge our current notion of ABE metabolic network structure. Thus, clostridial ABE fermentation still poses theoretical as well as experimental challenges which are best approached in close collaboration between modellers and experimentalists
Modulation tumorassoziierter Angiogenese- und EntzĂŒndungsmediatoren durch antiinflammtorisches (-)-Epigallocatechin-3-gallat und den IL-1-Rezeptorantagonisten in humanen Osteosarkomzellen
Experimental determination of the oxygen K shell fluorescence yield using thin SiO2 and Al2O3 foils
Synthesis of maleic and pHthalic anhydrides from the mixture of cyclopentene and 1-pentene
Focusing of soft X ray radiation and characterization of the beam profile enabling X ray emission spectrometry at nanolayered specimens
Experimental determination of line energies, line widths and relative transition probabilities of the Gadolinium L x ray emission spectrum
In this work the most intense x ray lines of the L emission spectrum of gadolinium with respect to line energies, natural line widths, and relative transition probabilities were investigated using monochromatized synchrotron radiation. The measurements were realized in the PTB laboratory at BESSY II by means of an in house built von Hamos spectrometer based on up to two full cylinder HAPG mosaic crystals. The von Hamos spectrometer is calibrated by means of elastically scattered photons from the employed synchrotron radiation beamline leading to a well defined energy scale and an experimentally determined spectrometer response. A selective excitation of the gadolinium L subshells was carried out to ensure a robust deconvolution of neighboring emission lines of different L subshells. The experimental results are discussed in the context of existing data from common databases and published values since significant deviations, especially for the L and L emission lines, are observed. We further substantiate and discuss two satellite lines at the low energy side of the L and L emission lines arising from the N4,5 subshel
The anisotropy in the optical constants of quartz crystals for soft Xârays
The refractive index of a yâcut SiO2 crystal surface is reconstructed from orientationâdependent soft Xâray reflectometry measurements in the energy range from 45 to 620â
eV. Owing to the anisotropy of the crystal structure in the (100) and (001) directions, a significant deviation of the measured reflectance at the Si L2,3 and O K absorption edges is observed. The anisotropy in the optical constants reconstructed from these data is also confirmed by ab initio BetheâSalpeter equation calculations for the O K edge. This new experimental data set expands the existing literature data for quartz crystal optical constants significantly, particularly in the nearâedge regions.The refractive index of a yâcut SiO2 crystal surface is reconstructed from polarizationâdependent soft Xâray reflectometry measurements in the energy range from 45 to 620â
eV. The reconstructed anisotropy in the optical constants is also confirmed by ab initio BetheâSalpeter equation calculations of the O K edge.
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