122 research outputs found
Photoexcitation of mass/charge selected heminâș, caught in helium nanodroplets
We report on a method by which mass/charge selected ions are picked up from a linear ion trap by liquid helium droplets. The size distributions of the doped droplets are measured via acceleration experiments. Depending on the source temperature, droplet sizes ranging from tens of thousands to several million helium atoms are obtained. Droplets doped with hemin, an iron containing porphyrin molecule, in the charge state +1 are then investigated using laser spectroscopy. It is observed that excitation with UV/VIS light can lead to ejection of the ion from the droplet. For doped droplets with a median size of B150 000 helium atoms, the absorption of two photons at 380 nm is needed for ejection to become efficient. When droplets become smaller, the ejection efficiency is observed to strongly increase. Monitoring the ejection yield as a function of excitation wavelength can be used to obtain the optical spectrum of heminâș. Compared to the spectrum of free gas-phase heminâș at room temperature, the narrower and shifted to the blue
Mathematical and computer modeling of electro-optic systems using a generic modeling approach
The conventional approach to modelling electro-optic sensor systems is to develop separate models for individual systems or classes of system, depending on the detector technology employed in the sensor and the application. However, this ignores commonality in design and in components of these systems. A generic approach is presented for modelling a variety of sensor systems operating in the infrared waveband that also allows systems to be modelled with different levels of detail and at different stages of the product lifecycle. The provision of different model types (parametric and image-flow descriptions) within the generic framework can allow valuable insights to be gained
Imaging Molecular Structure through Femtosecond Photoelectron Diffraction on Aligned and Oriented Gas-Phase Molecules
This paper gives an account of our progress towards performing femtosecond
time-resolved photoelectron diffraction on gas-phase molecules in a pump-probe
setup combining optical lasers and an X-ray Free-Electron Laser. We present
results of two experiments aimed at measuring photoelectron angular
distributions of laser-aligned 1-ethynyl-4-fluorobenzene (C8H5F) and
dissociating, laseraligned 1,4-dibromobenzene (C6H4Br2) molecules and discuss
them in the larger context of photoelectron diffraction on gas-phase molecules.
We also show how the strong nanosecond laser pulse used for adiabatically
laser-aligning the molecules influences the measured electron and ion spectra
and angular distributions, and discuss how this may affect the outcome of
future time-resolved photoelectron diffraction experiments.Comment: 24 pages, 10 figures, Faraday Discussions 17
Coulomb explosion imaging of small organic molecules at LCLS.
Fragmentation of small organic molecules by intense few-femtosecond X-ray free-electron laser pulses has been studied using Coulomb explosion imaging. By measuring kinetic energies and emission angles of the ionic fragments in coincidence, we disentangle different fragmentation pathways, for certain cases can reconstruct molecular geometry at the moment of explosion, and show how it depends on LCLS pulse duration
Konnten die GrundsÀtze der gemeindenahen Versorgung realisiert werden? Eine Bestandsaufnahme der Versorgungssituation alter Menschen aus medizinsoziologischer Sicht
Garms-HomolovĂĄ V, HĂŒtter U, Schaeffer D. Konnten die GrundsĂ€tze der gemeindenahen Versorgung realisiert werden? Eine Bestandsaufnahme der Versorgungssituation alter Menschen aus medizinsoziologischer Sicht. In: Kleiber D, Filsinger D, eds. Altern - bewĂ€ltigen und helfen. Heidelberg: R. Asanger; 1989: 75-85
Model Combustor to Assess the Oxidation Behavior of Ceramic Materials Under Real Engine Conditions, ASME-Paper No
ABSTRACT A further increase of thermal efficiency and a reduction of the exhaust emissions of ground based gas turbines can be achieved by introducing new high temperature resistant materials. Therfore, ceramics are under international development. They offer excellent strengths at room and elevated temperatures. For gas turbine combustor applications, however, these materials have to maintain their advantageous properties under hostile environment. For the assessment and comparison of the oxidation behavior of different nonoxide ceramic materials a test rig was developed at the Institute for Thermal Turbomachinery (ITS), University of Karlsruhe, Germany. The test rig was integrated into the high temperature/ high pressure laboratory. A ceramic model combustion chamber was designed which allowed the exposure of standard four-point flexure specimens to the hot combustion gas flow. Gas temperatures and pressures could be varied in a wide range. Additionally, the partial steam pressure could be adjusted to real combustor conditions. The present paper gives a detailed description of the test rig and presents results of 100 hours endurance tests of ceramic materials at 1400°C. The initial strengths and the strengths after oxidation tests are compared. In addition to this, photographs illustrating the changes of the material's microstructure are presented
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