The influence of processing on the microstructure and the microwave properties of Co-F-codoped barium strontium titanate thick-films

The influence of processing on the microstructure and the dielectric properties of Co-F-codoped Ba_0.6Sr_0.4TiO₃ (BST) thick-films has been investigated. BST powders with different particle sizes were prepared and applied on alumina substrates by screen-printing. The resulting thick-films were sintered at different holding times and characterized with respect to their microstructure and microwave properties. The microstructure of the thick-films shows a clear dependency on sintering time and initial particle size. In addition to grain growth, the formation of a secondary phase is observed at the interface between substrate and BST with increasing sintering time. The dielectric characterization at microwave frequencies shows an increase of tunability with larger grain size while the dielectric loss is even lowered. This shows the strong influence of the microstructure on the material properties and the possibility of tailoring the material through specific processing.     

Integration von Energiemarkt und Verteilnetzbetrieb durch einen Flexibility Operator

The growing share of volatile distributed generation in the electric power grids results in increased local network utilisation and challenges the conventional strategies for maintaining the system balance. While grid extensions and smart grid solutions are considered for network utilisation issues, new market mechanisms are in focus for the balancing challenge. It can be expected that distributed generators on one hand will be able to supply only part of their available power to the grid in peak times, and on the other hand will have (potentially changing) contracts with different trans-regional virtual power plants. Against this background it will be necessary to define rules dealing with expected network access conflicts. One strategy also followed in this work is to find market mechanisms that support economically efficient network extension. Such mechanisms will have to include local flexibility markets that allow for compensating network bottlenecks. This work proposes strategies and technical interfaces for coordinating market and grid operation by means of a “Flexibility Operator”. Its integration into a holistic smart grid concept is discussed.     

The angle between the anticodon and aminoacyl acceptor stems of yeast tRNA(Phe) is strongly modulated by magnesium ions

Many tRNAs undergo tertiary folding transitions at temperatures well below the main thermally induced (hyperchromic) transition. Such transitions are essentially isochromic and isoenthalpic and display an absolute requirement for divalent cations; however, the nature of the structural transition is not known for any tRNA. Using a combination of transient electric birefringence (TEB) and gel electrophoretic measurements, we have characterized the influence of magnesium ions on the apparent angle between the anticodon and acceptor stems of a yeast tRNA(Phe) construct. TEB is a particularly sensitive method for quantifying the bends introduced in RNA by various nonhelix elements. In the current instance, the tRNA construct comprises an unmodified tRNA(Phe) molecule in which the anticodon and acceptor stems have been extended by approximately 70 bp to more effectively "report" the interstem angles. Upon the addition of sub-millimolar concentrations of magnesium ions, the tRNA core undergoes a substantial rearrangement in tertiary structure, passing from an open form with an apparent interstem angle of approximately 150 degrees to a conformation with an interstem angle of approximately 70 degrees (200 microM Mg2+). Further addition of magnesium ions results in a minor adjustment of the apparent interstem angle to approximately 80-90 degrees, in line with earlier results. Finally, the magnesium-induced structural transition is essentially isochromic, in agreement with previous observations with native tRNAs. The current results suggest that changes in local divalent ion concentration in the ribosome could profoundly affect the global conformations of tRNAs during the translation cycle.     

Molecular Origin of the Charge Carrier Mobility in Small Molecule Organic Semiconductors

Small‐molecule organic semiconductors are used in a wide spectrum of applications, ranging from organic light emitting diodes to organic photovoltaics. However, the low carrier mobility severely limits their potential, e.g., for large area devices. A number of factors determine mobility, such as molecular packing, electronic structure, dipole moment, and polarizability. Presently, quantitative ab initio models to assess the influence of these molecule‐dependent properties are lacking. Here, a multiscale model is presented, which provides an accurate prediction of experimental data over ten orders of magnitude in mobility, and allows for the decomposition of the carrier mobility into molecule‐specific quantities. Molecule‐specific quantitative measures are provided how two single molecule properties, the dependence of the orbital energy on conformation, and the dipole‐induced polarization determine mobility for hole‐transport materials. The availability of first‐principles based models to compute key performance characteristics of organic semiconductors may enable in silico screening of numerous chemical compounds for the development of highly efficient optoelectronic devices.     

Biodegradation and product identification of [14C]hexabromocyclododecane in wastewater sludge and freshwater aquatic sediment

In a previous study the biodegradation of hexabromocyclododecane (HBCD) was reported to occur under realistic environmental concentrations in soils and freshwater aquatic sediments with biotransformation half-lives ranging from approximately 2 days to 2 months. In this study we extend our knowledge as to the environmental behavior of HBCD with respect to the fate of the three major diastereomers of HBCD (alpha, beta, and gamma) as well as to the identification of major intermediate metabolites formed during degradation. Substantial biological transformation of the alpha-, beta-, and gamma-[14C]HBCD diastereomers was observed in wastewater (i.e., digester) sludge and in freshwater aquatic sediment microcosms prepared under aerobic and anaerobic conditions. Concomitant with the loss of [14C]HBCD in these matrixes there was a concurrent production of three [14C]products. Using a combination of high performance liquid chromatography atmospheric pressure photoionization mass spectrometry and gas chromatography electron impact ionization mass spectrometry these metabolites were identified as tetrabromocyclododecene, dibromocyclododecadiene, and cyclododecatriene. We propose that HBCD is sequentially debrominated via dihaloelimination where at each step there is the loss of two bromines from vicinal carbons with the subsequent formation of a double bond between the adjacent carbon atoms. These results demonstrate that microorganisms naturally occurring in aquatic sediments and anaerobic digester sludge mediate complete debromination of HBCD.