Thermally driven acoustic oscillations, part IV: Tubes with variable cross-section

The problem of thermally driven acoustic oscillations is treated for tubes with variable cross-section, with particular emphasis on the possible reduction of the necessary temperature ratio for excitation. Tubes with optimal conditions in the vicinity of the temperature jump, and with big cross-sections in parts with constant temperature are found to give the best performance in this respect. Included in the family of devices which were treated is the classical Sondhauss-tube. Experiments which give a striking confirmation of the theory are reported.     

Structure-based validation of the 3D-QSAR technique MaP

For three target proteins with different binding pocket characteristics (size and shape, hydrophobicity, hydrogen-bonding) a structure-based validation of the translationally and rotationally invariant 3D-QSAR technique MaP is performed (MaP: Mapping Property distributions of molecular surfaces). The structure-based validation procedure comprises two steps: first, QSAR models are derived without using the information of the target protein. Second, the models are back-projected into the crystal structure of the binding pockets and interpreted. It is demonstrated that MaP is able to identify characteristics important for ligand binding in the cases studied here. Moreover, it is demonstrated that MaP is a versatile 3D-QSAR technique since good, predictive models could be obtained for all three data sets showing distinct characteristics.     

Preparation and characterization of regioisomerically pure 1,7-disubstituted perylene bisimide dyes

A detailed study on bromination and subsequent imidization of perylene bisanhydride with cyclohexylamine is reported. The present results reveal that previously reported 1,7-difunctionalized perylene bisimides are presumably contaminated with the respective 1,6 regioisomers. N,N'-Dicyclohexyl-1,7-dibromoperylene bisimide 1,7-3 is obtained for the first time in isomerically pure form, and its structure is unequivocally confirmed by X-ray analysis. By using regioisomerically pure 1,7-dibromoperylene bisimide 1,7-3, 1,7-dipyrrolidinylperylene bisimides 4a-c and 1,7-dipyrrolidinylperylene bisanhydride 5 as well as the unsymmetrically difunctionalized 1-bromo-7-pyrrolidinyl- and 1-cyano-7-pyrrolidinylperylene bisimides 7 and 8 are synthesized in good yield.     

MRI observation of heavy metal transport in aquifer matrices down to sub-mg quantities

In this contribution, we report results from MRI studies of the propagation of heavy metal ions through columns packed with sandy aquifer materials. Both sorption of low concentrations of heavy metal ions from water flowing through the column and the formation of sorption traces produced from initially localized higher concentrations of heavy metal ions, and the remobilisation of adsorbed ions with time and changing hydrochemical conditions were studied. Multislice spin-echo and FLASH techniques were used for the imaging experiments. Advantages and problems of the different imaging protocols for the study of aquifer materials are discussed.     

Femtosecond transient absorption with chirped pump and supercontinuum probe: Perturbative calculation of transient spectra with general lineshape functions, and simplifications

Femtosecond transient UV/vis absorption spectra of molecules in solution show vibronic structure initially while pump and probe pulses overlap, superimposed on bands which broaden and shift on several time scales. Third-order perturbation theory is used simulate and understand such spectra under experimental conditions, i.e., with chirped pump pulses and 40–80 fs pump/probe correlation time. The electronic system is coupled to a solvent bath whose fluctuations enter through a lineshape function g(t). This approach has two advantages. (i) In the general case when g(t) is modelled realistically it provides a distinction of coherent and sequential contributions to early transient spectra. The time-zero stimulated emission band can be extracted, giving access to the relaxation function for the emission frequency. (ii) For limiting forms of g(t) corresponding to the Bloch approximation and to inhomogeneous broadening the threefold time integrals underlying the theory reduce to a single integral. In such cases the lineshape formulation of transient absorption spectra can be used for data fitting.