Optimal Data Selection for Piezoelectric Material Characterization

In the simulation and design of piezoelectric transducers the exact knowledge of the entries in the material tensors - the elastic, dielectric and piezoelectric coupling coefficients - is an important prerequisite. Our task is the identification of these coefficients from indirect measurements, namely electric impedance data at different frequencies. This leads to a parameter identification problem for a system of coupled PDEs, which we solve by regularized Newton iterations. A crucial issue is the selection of frequencies at which measurements are taken. Here, we discuss the problem of choosing these frequencies in an optimal way to preserve efficiency of our identification scheme while improving reliability of the reconstruction results. For this purpose, we formulate this task as an optimization problem with PDE constraints and propose two approaches for its solution. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Waterpipe smoke: A considerable source of human exposure against furanic compounds

Smoking of waterpipes became increasingly popular in the Western hemisphere in recent years. Yet, up to now only little is known about the health hazards and on the composition of waterpipe smoke. To obtain more information on the ingredients present in waterpipe smoke we utilized two different approaches. Based on headspace-solid-phase microextraction–gas chromatography–mass spectrometry (HS-SPME–GC–MS) instrumentation we identified new compounds present in the waterpipe smoke. Additional reversed-phase-high performance liquid chromatography–diode array detection (RP-HPLC–DAD) then led us to perform reliable quantification of the newly detected chemical species. Upon identification of a range of different furanic compounds such as 5-(hydroxymethyl)-2-furaldehyde (HMF), 2-furaldehyde, and others, we developed an easy-to-perform and fast RP-HPLC–DAD method to quantify these compounds in the complex matrix of waterpipe smoke. The detection limits range from 0.04 μg for HMF to 7.1 μg for 3-furan methanol per smoking session. Linearity, intra- and inter-day precision and recovery were determined and proved excellent. We analyzed 5 waterpipe tobacco brands and found up to 62.3 ± 11 mg of HMF generated during one waterpipe smoking session. The applied smoking protocol comprised 171 puffs of 530 mL each and 2.6 s duration every 20 s. Our results reveal that waterpipe smoking constitutes a major source of HMF exposure. Furthermore, we found a distinct filter effect of the bowl water for all furanic compounds investigated except HMF.     

BINAP: rhodium–diolefin complexes in asymmetric hydrogenation

The complexes [Rh((S)-BINAP)(COD)]BF₄ 1, [Rh((S)-BINAP)(NBD)]BF₄ 2, [Rh((R)-BINAP)(COD)]OTf 3, [Rh((R)-BINAP)(NBD)]OTf 4, and [Rh((R)-BINAP)(COD)]BArF 5 were synthesized, and 1–4 were analyzed by single crystal X-ray crystallography. The transformation of these precatalysts into hydrogenation-active species was investigated as well as the hydrogenation of prochiral olefins. In particular, this series of transformations was investigated with regard to solvent and counterions.