Technical University of Berlin

About: Technical University of Berlin is a education organization based out in Berlin, Germany. It is known for research contribution in the topics: Laser & Catalysis. The organization has 27292 authors who have published 59342 publications receiving 1414623 citations. The organization is also known as: Technische Universität Berlin & TU Berlin.

Ultra-efficient ionization of heavy atoms by intense X-ray free-electron laser pulses

Abstract: X-ray free-electron lasers provide unique opportunities for exploring ultrafast dynamics and for imaging the structures of complex systems. Understanding the response of individual atoms to intense X-rays is essential for most free-electron laser applications. First experiments have shown that, for light atoms, the dominant interaction mechanism is ionization by sequential electron ejection, where the highest charge state produced is defined by the last ionic state that can be ionized with one photon. Here, we report an unprecedentedly high degree of ionization of xenon atoms by 1.5 keV free-electron laser pulses to charge states with ionization energies far exceeding the photon energy. Comparing ion charge-state distributions and fluorescence spectra with state-of-the-art calculations, we find that these surprisingly high charge states are created via excitation of transient resonances in highly charged ions, and predict resonance enhanced absorption to be a general phenomenon in the interaction of intense X-rays with systems containing high-Z constituents. Researchers create high ionization states, up to Xe36+, using 1.5 keV free-electron laser pulses. The higher than expected ionization may be due to transient resonance-enhanced absorption and the effect may play an important role in interactions of intense X-rays with high-Z elements and radiation damage.

Mn–Na2WO4/SiO2 as catalyst for the oxidative coupling of methane. What is really known?

Abstract: Mn–Na2WO4/SiO2 is one of the very few catalysts for the oxidative coupling of methane, whose stability over extended times on stream has been reported by different research groups. The high stability turned Mn–Na2WO4/SiO2 into an object of research, despite the rather complex composition and structure. The nature of the active site or the active phase is unclear, in spite of the research on this catalytic system. This manuscript tries to critically summarize the literature on this system and to discuss the available information about the relationship of structure and activity.

Rheological Evidence for a Dynamical Crossover in Polymer Melts via Nonequilibrium Molecular Dynamics

Abstract: A certain "critical" molecular weight controls rheological properties of the multibead finitely extensible nonlinear elastic (FENE) chain model polymer melt. The rheological crossover manifests itself in a change of power law behavior for the viscous properties at a critical number of beads per chain N(c) = 100+/-10. This finding confirms a newly proposed relationship between dimensionless critical weight, characteristic length, and flexibility which we obtain as a side result. Results further suggest that the entanglement molecular weight N(e) for the flexible FENE chain model could be comparable in size or even larger than its critical molecular weight N(c).