Wolfgang Christen

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Computer simulations and experiments have been performed to quantify the effects of nozzle shape and skimmer placement on high-density supersonic jets. It is shown that the on axis beam intensity achieved is much higher than intensity achieved using standard sonic nozzles. Changes in skimmer design and positioning are required to allow this intense jet to(More)
Pulsed, supersonic beams of pure carbon monoxide and carbon dioxide at stagnation conditions above their critical point have been investigated by time-of-flight measurements as a function of pressure and temperature. Although both molecules form clusters readily in adiabatic expansions, surprisingly large speed ratios (above 100) indicative of very low(More)
Crystallization processes under different conditions are of fundamental interest in chemistry, pharmacy, and medicine. Therefore, we have studied the formation of micro- and nanosized crystals using water-caffeine (1,3,7-trimethyl-1 H-purine-2,6(3 H,7 H)-dione) solutions under ambient conditions as a relevant model system. When droplets of an aqueous(More)
We describe an experimental setup for supersonic jet expansions of supercritical fluids. It is characterized by well-defined thermodynamic values to allow systematic investigations of pressure and temperature effects on molecular beam parameters. The design permits stagnation temperatures T(0)=225-425 K with a thermal stability DeltaT(0)<30 mK and(More)
We describe a generally applicable method for the experimental determination of stationary flow conditions in pulsed supersonic beams, utilizing time-resolved electron induced fluorescence measurements of high pressure jet expansions of helium. The detection of ultraviolet photons from electronically excited helium emitted very close to the nozzle exit(More)
We report on the concept, progress and status of the new project Distributed Open Access Reference Citations Services, DOARC . The emphasis is to exploit especially the Open Access documents on Institutional Repositories: analyzing their reference lists for citations, analyzing the full text for research field specific two-word shingles, and use this for(More)
The dissolution of the primary nucleobases in supercritical fluids has been investigated using pulsed molecular beam mass spectrometry. Due to the low critical temperatures of ethylene and carbon dioxide, their adiabatic jet expansion permits transferring thermally sensitive solutes into the gas phase. This feature is particularly attractive for(More)
We introduce a straightforward experimental approach for determining the mean flow velocity of a supersonic jet with very high precision. While time measurements easily can achieve accuracies of Δt/t ≤ 10(-4), typically the absolute flight distances are much less well-defined. This causes significantly increased errors in calculations of the mean flow(More)
In der II . lVfitteflung (ds. Arch. Bd. 233, S. 43) wurde in Bes~atigung yon Versuehen Biittners nachgewiesen, dab ~uskeln, deren sympathisehe Innervation einige Tage vorher ausgescha]tet worden war, an Glykogen zunehmen. Daraus geht hervor, dab in der Norm der Sympathicus einen die Glykogenbildung hemmenden ~onischen Einflul3 ausiibt, tIierauf allein(More)
Smooth and defect-rich Ru(0001) surfaces prepared under ultrahigh-vacuum (UHV) conditions have been loaded with oxygen under high-pressure (p </= 1 bar) and low-temperature (T < 550 K) conditions. On these surfaces the CO oxidation reaction has been investigated by means of thermal desorption spectroscopy (TDS), ultraviolet photoelectron spectroscopy (UPS)(More)