Students' seminar

The conductive polymer poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS) is of great interest for a variety of applications in flexible and stretchable electronics. However, to advance novel applications on appropriate substrates, innovative and reliable methods for processing conductive polymers are still needed. Here, we present a fast, dependable, and easy PEDOT:PSS transfer-printing method on flexible, transparent, and biodegradable polyvinyl alcohol (PVA) targets. In contrast to previous work, this method neither depends on acid nor doping treatments nor surface soaking treatments. Furthermore, our approach is compatible with common strategies to induce stretchability and increase the conductivity of PEDOT:PSS. Key to this method is the chemical engineering of hydrogen bonds. To adjust the mechanical properties, glycerol is incorporated in varying amounts into the PVA targets. Additionally, a novel methodology to pattern PEDOT:PSS thin films is established, using an oxygen-plasma treatment. These patterned films can be transfer-printed, employing the herein present process. Lastly, the water-soluble targets allow for environmental-friendly decomposition. [more]

In addition to human impacts on global climate due to greenhouse gas emissions, natural emission sources from vegetation and combustion influence atmospheric composition and processes. This project aims to better understand the relationship between natural emissions and plant stress factors such as temperature, light and water availability, or ambient concentrations of irritant gases. In Addition, resulting feedback mechanisms of biogenic carbon and VOC emissions will be analyzed using the refined EMAC (ECHAM5/MESSy Atmospheric Chemisty Model). For this purpose, EMAC is extended by the implementation of the land surface model JSBACH (Jena Scheme for Biosphere-Atmosphere Coupling in Hamburg) to a comprehensive Earth system model. This extension enables EMAC to simulate not only atmospheric transport processes and chemistry, but also soil and vegetation processes. [more]

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Speleothem d18O values depend on a complex interplay of various processes occurring in the atmosphere, the soil and karst above the cave as well as during precipitation of speleothem calcite. Thus, the relationship between speleothem d18O values and climate parameters, such as local and supra-regional temperature and precipitation patterns, is in many cases not straightforward. Here we present a set of global simulations for different time periods (Modern Day, LGM, MIS3, …) with a mean duration of 20 years, performed with the EMAC atmospheric chemistry general circulation model, being enhanced with stable water isotope diagnostics. The model resolution comprises of a horizontal grid with a maximum resolution of 0.88° × 0.88° (T106) and a vertical resolution of 31 model levels (top level at 0.01 hPa). The simulated d18O values in precipitation were converted into synthetic speleothem d18O records by accounting for the effects of evapotranspiration and infiltration using model-internal empirical evapotranspiration submodels as well as the drip&#2;water-to-calcite fractionation equation by Tremaine et al. (2011). We then calculated mean speleothem d18O values on an annual and seasonal basis, weighted by the amount of precipitation and infiltration (pw-d 18O, iw-d 18O), respectively. The synthetic speleothem d18O records were compared with speleothem d18O records from the Speleothem Isotopes Synthesis and Analysis Working group (SISAL) database. In general, the model setup is capable of adequately simulating the global pattern of d18O values in precipitation. The synthetic speleothem d18O records clearly benefit from weighting by the amount of precipitation and, partly, even more from weighting by infiltration (i.e., the application of an evapotranspiration model). This is obvious by the better agreement of iw-d18O speleothem records with the SISAL data for regions with an infiltration-to-precipitation ratio <0.7 (e.g., the Mediterranean Region). In temperate regions, such as Central Europe, the iw-d18O is approximately similar to the corresponding pw-d18O. Thus, infiltration in these regions seem to be less influenced by evapotranspiration and surface runoff. The evapotranspiration model but limitations when calculating evapotranspiration in extremely arid and/or cold areas, possibly resulting in biased iw-d18O values. Commonly, the climate of these regions is too harsh for speleothem growth, and therefore currently not subject of this study. [more]

Almost all information in the world is processed and transmitted either by electric currents or by photons. Spin waves, the fundamental excitations of magnetic media, could perform some of these tasks in a much more efficient and practical way. I will introduce the concept of spin-wave based computing and provide insight into the fundamental research of hybrid electric-spin-wave devices for such applications. In this context I will present the optical method used to investigate these systems, namely, micro-focused Brillouin-light-scattering spectroscopy. [more]

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Supramolecular assemblies in nature are the embodiment of creating function through structure formation. In recent years, these complex natural architectures have inspired the development of materials for the in-situ formation of synthetic nanostructures inside living cells. Synthetic intracellular assemblies can be used to modulate cellular processes, however, their effects on metabolism and three-dimensional cell networks have not been widely explored. Herein, we present bioresponsive kinked peptides that can undergo a multistep transformation into self-assembling linear peptides in living cells. The intracellular peptide assembly causes metabolic disruption and rapid cell death. This work showcases the potential use of bioresponsive nanomaterials as supramolecular anticancer drugs via the construction of synthetic architectures inside living cells. [more]