Tunable haptotropic metal migration in fused arenes: towards organometallic switches

Tricarbonyl chromium complexes of naphthalene derivatives are synthesized by chromium-templated [3 + 2 + 1]-benzannulation and subjected to thermally induced haptotropic rearrangement experiments. Thermodynamic and kinetic parameters for the metal shift demonstrate the influence of the arene substitution pattern. In turn, the chromium template may be tuned as well by phosphorus coligands which allow to accelerate or slow down the isomerization process; this effect quantitatively reflects the steric and electronic properties of the coligand sphere. Proper adjustment of the template allows for a photo-induced reverse migration of the chromium moiety which results in a switchable organometallic device. Experiments with enantiopure arene chromium complexes indicate a stereospecific metal migration. The rearrangement proceeds by an intramolecular mechanism in both directions. Haptotropic isomerization reactions are not limited to bicyclic arenes and can be extended from naphthalenes to phenanthrene or tetra- and pentacyclic heteroarene systems.     

New ABC core for the synthesis of nonsymmetric star molecules

[reaction: see text] An ABC core has been synthesized, with two orthogonal protecting groups (PG). This new multifunctional unit allows building of star-shaped molecules with up to three different moieties. The synthesis of a star-shaped mesogen based on an oligobenzoate scaffold with three arms of different lengths is demonstrated.     

Design and implementation of a MEMS microphone array system for real-time speech acquisition

Despite many attractive features and the potential for capturing sound in challenging acoustic environments, arrays with a large number of microphones have for a long time been discarded as a practical solution for speech acquisition. This is, among other reasons, due to the high production and computational costs. Only a few realizations of large microphone array systems have been documented, mainly for research and instrumentation use. The advent of MEMS microphones and computationally powerful off-the-shelf hardware has created new possibilities for microphone array development. We investigate a real life application, specifically the case of live sports broadcast, and the requirements that a such application imposes on a microphone array system. We present a system architecture of the first large (300 element circular array with a diameter of 2 m) MEMS microphone array system. In the proposed system, the latest technological advances are utilized to create a user-friendly array control interface. The array’s performance is examined in an anechoic chamber and on a crowded basketball field, and finally compared with existing solutions. The results illustrate the potential of a large MEMS microphone array as part of the technological development in sound acquisition for entertainment and security applications.     

Taming the Friedel-Crafts reaction: organocatalytic approach to optically active 2,3-dihydrobenzofurans

Fine-tuning: Three types of optically active trans-2,3-disubstituted-2,3-dihydrobenzofurans having three contiguous stereogenic centers can be efficiently accessed by one-pot reaction cascades (see scheme; TMS = trimethylsilyl). High substitution diversity of the final products can be achieved from the same common precursors by fine-tuning of their reactivity through simple structural modifications.     

Literatur

Ohne Zusammenfassung     

Viscoelastic modelling and experimental results of a dielectric electro-active polymer diaphragm actuator

Common actuating principles e.g. solenoids or piezo-elements have mostly exploited their potential as electromechanical transducers. A new technology based on Dielectric Electro-active Polymers (DEAPs) enables major progress in efficiency and functionality for actuators. In order to use the advantages of this new technology in a feasible application, a silicone based DEAP diaphragm actuator was tested experimentally. Here, the mechanical properties of the fundamental parts of the DEAP diaphragm actuator, namely the stressstrain behaviour of an equibiaxially pre-stretched hyperelastic polymer and the mechanical response of a DEAP diaphragm actuator, were determined by appropriate test benches. The investigated DEAP diaphragm actuator consists of a dielectric, which corresponds to a thin elastic silicone film sandwiched between two compliant electrodes. Furthermore, DEAPs are pre-stretched, actually up to five times their in-plane dimensions, in order to improve their performance. In that context, the influence of the pre-stretched state on the actuator performance was investigated. In addition, a viscoelastic finite-element model of the electromechanical system has been developed and validated with the experimental results. The mechanical part of the DEAP diaphragm actuator was realized with an incompressible isotropic elastic model, whereas the electrical part was approximated with a circular parallel-plate capacitor. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)