Westflische Wilhelms University

Friedrich-Wilhelm-Lübke-Koog, Germany

Westflische Wilhelms University

Friedrich-Wilhelm-Lübke-Koog, Germany
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Frekers D.,Westflische Wilhelms University | Lennarz A.,Westflische Wilhelms University | Puppe P.,Westflische Wilhelms University | Thies J.H.,Westflische Wilhelms University
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2010

Self-supporting gallium targets (natGa, 69Ga, 71Ga) with areal densities varying between 2 and 4 mg/cm2 have been produced for a medium-energy (3He, t) nuclear scattering experiment. A new method for target preparation, involving melting, squeezing and shock-freezing the material has been employed. The special and peculiar properties of the gallium metal material are described, which necessitate special procedures for thin foil and thin target production. © 2010 Elsevier B.V. All rights reserved.

Ashley J.W.,Arizona State University | Robinson M.S.,Arizona State University | Hawke B.R.,University of Hawaii at Manoa | Van Der Bogert C.H.,Westflische Wilhelms University | And 7 more authors.
Journal of Geophysical Research E: Planets | Year: 2012

New geologic sketch maps and digital elevation models for King crater and the surrounding lunar farside highlands were created from Lunar Reconnaissance Orbiter Camera (LROC) Wide-angle Camera (WAC) and Narrow Angle Camera (NAC) images. NAC images reveal that high volume impact melt accumulations exhibit evidence of dynamic processes during and following emplacement that resulted in downwarped zones, and other morphologic anomalies visible at the 50 cm pixel scale. Among the most significant of these forms are negative relief features, some of which may represent evidence for near-surface caverns, offering points of access to subsurface environments and possible shelter from surface hazards. Other negative relief features may represent regions of extension and separation in response to possible subsurface drainage, together with isostatic readjustments, contraction, and/or compaction, in the cooling impact melt. Crater counts on the continuous ejecta blanket suggest a Late Eratosthenian to Copernican age for King crater, which is older than the estimate of Young (1977), but consistent with those of others. © 2012. American Geophysical Union. All Rights Reserved.

Muller K.,Westflische Wilhelms University | Albach D.C.,Carl von Ossietzky University
Journal of Molecular Evolution | Year: 2010

The evolutionary rate at which DNA sequences evolve is known to differ between different groups of organisms. However, the reasons for these different rates are seldom known. Among plants, the generation-time hypothesis, which states that organisms that reproduce faster also have more DNA substitutions per time, has gained most popularity. We evaluate the generation-time hypothesis using 131 DNA sequences from the plastid trnLF region and the nuclear ribosomal ITS region of the genus Veronica (Plantaginaceae). We also examine the alternative hypothesis that a higher substitution rate is correlated with selfing breeding system. Selfing is associated with annual life history in many organisms and may thus often be the underlying reason for observed correlations of annual life history with other characters. We provide evidence that annual life history is more likely to be the responsible factor for higher substitution rates in Veronica than a selfing breeding system. Nevertheless, the way in which annual life history may influence substitution rate in detail remains unknown, and some possibilities are discussed. © 2009 Springer Science+Business Media, LLC.

Rosenfeldt A.C.,Westflische Wilhelms University | Gohler B.,Westflische Wilhelms University | Zacharias H.,Westflische Wilhelms University
Journal of Chemical Physics | Year: 2010

Time-resolved two-photon photoemission is applied to investigate electron dynamics in multiple monolayers (MLs) of ordered fullerite on a copper substrate. The experimental data are analyzed assuming coupled excited state dynamics. Rate equations fitted to these dynamics yield lifetimes of about 80 ps for the lowest unoccupied molecular orbital (LUMO), about 1.2 ns for the singlet exciton and 22 s for the triplet exciton at a surface temperature of 140 K. For trapped triplet excitons lifetimes up to 200 s are observed. An increased excitation fluence reduces the lifetime of the excitons due to annihilation. An increased sample temperature slightly reduces the lifetime of the triplet exciton. There is no evident dependence of the exciton lifetimes on the pump photon energy in the range of hv = 2.9 to 3.3 eV. A dependence on the layer thickness (10-20 ML) is not observed as long as more than 9 ML are prepared. © 2010 American Institute of Physics.

Kroesen S.,Westflische Wilhelms University | Horn W.,Westflische Wilhelms University | Denz C.,Westflische Wilhelms University
2011 Conference on Lasers and Electro-Optics Europe and 12th European Quantum Electronics Conference, CLEO EUROPE/EQEC 2011 | Year: 2011

Tuneable optical delaying of short pulses is one of the key components for future all-optical telecommunication networks and information processing systems. Important applications include optical buffering, synchronisation, optical delay lines or jitter correction [1]. One dimensional resonant structures such as Fiber Bragg gratings (FBG) provide large group index enhancements and strong dispersion far away from any material resonance. Beside their small size and compatibility to fiber optics they offer low loss narrow frequency rejection and the possibility to operate at room temperature. The main disadvantage of these systems is that once these types of gratings have been induced, possibilities to manipulate the spectral response are limited to mechanical strain or temperature tuning. In this work we present a versatile holographic approach to dynamically implement gratings into photorefractive LiNbO3 crystals. Subsequently, we demonstrate control of the group velocity these gratings that are dynamically addressed and phase-engineered to obtain complex structures as e.g. multiple p phase-shifted and super-structured gratings. © 2011 IEEE.

Ferse I.,Westflische Wilhelms University | Langlitz M.,Westflische Wilhelms University | Kleigrewe K.,Westflische Wilhelms University | Rzeppa S.,Westflische Wilhelms University | And 4 more authors.
Natural Product Research | Year: 2012

In this study, 10 already described secondary metabolites and 2 unknown metabolites were identified in an extract of Monascus purpureus by high-performance liquid chromatography-diode array detection. The unknown metabolites were isolated and their chemical structures were elucidated. The new metabolites possess the molecular formulas C21H27NO 4 and C23H31NO4. They were named monascopyridines E and F due to their pyridine backbone. The cytotoxicity of the new compounds was studied using immortalised human kidney epithelial cells displaying IC50 values in the micromolar range. © 2012 Copyright Taylor and Francis Group, LLC.

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