DNS and Experiment of a Turbulent Channel Flow with StreamwiseRotation - Study of the Cross Flow Phenomena

Modelling of rotating turbulent flows is a major issue in engineering applications. Intensive research has been dedicated to rotating channel flows in spanwise direction such as by [1], [2] to name only two. In this work a turbulent channel flow rotating about the streamwise direction is presented. The theory is based on the investigations of [4] employing the symmetry theory. It was found that a cross flow in the spanwise direction is induced. A series of direct numerical simulations (DNS) at different rotation numbers is carried out to examine these effects. Further, the results of the DNS are compared to the measuremets of a corresponding experiment. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

High temperature behavior of the chemical shift and nuclear spin relaxation of Se77 in solid selenium

The spin-lattice relaxation and the chemical shift (CS) anisotropy of Se⁷⁷ in selenium single crystals have been investigated between room temperature and the melting point (490 K). Over the entire temperature range, the CS-anisotropy is shown to be independent of the temperature. The temperature dependence of the spin-lattice relaxation is determined by phonon-induced fluctuation of the CS-tensor. Above 400 K, translational atomic diffusion causes a remarkable additional increase in the relaxation rate.     

PIV–LES analysis of channel flow rotating about the streamwise axis

The flow field of a channel rotating about the streamwise axis is analyzed experimentally and numerically. The current investigations were carried out at a bulk velocity based Reynolds number of Re_m = 2850 and a friction velocity based Reynolds number of Re_τ = 180, respectively. Particle-image velocimetry (PIV) measurements are compared with large-eddy simulation data to show earlier direct numerical simulation findings to generate too large a reverse flow region in the center region of the spanwise flow. The development of the mean spanwise velocity distribution and the influence of the rotation on the turbulent properties, i.e., the Reynolds stresses and the two-point correlations of the flow, are confirmed in both investigations. The rotation primarily influences those components of the Reynolds shear stresses, which contain the spanwise velocity component. The size of the correlation areas and thus the length scales of the flow generally grow in all three coordinate directions leading to longer structures. Furthermore, experimental results of the same channel flow at a significantly lower bulk Reynolds number of Re_{m, l} = 665, i.e., a laminar flow in a non-rotating channel, are introduced. The experiments show the low Reynolds number flow to become turbulent under rotation and to develop the same characteristics as the high Reynolds number flow.     

Propagation of a solitary fission wave

Reaction-diffusion phenomena are encountered in an astonishing array of natural systems. Under the right conditions, self stabilizing reaction waves can arise that will propagate at constant velocity. Numerical studies have shown that fission waves of this type are also possible and that they exhibit soliton like properties. Here, we derive the conditions required for a solitary fission wave to propagate at constant velocity. The results place strict conditions on the shapes of the flux, diffusive, and reactive profiles that would be required for such a phenomenon to persist, and this condition would apply to other reaction diffusion phenomena as well. Numerical simulations are used to confirm the results and show that solitary fission waves fall into a bistable class of reaction diffusion phenomena.     

Glycopeptide biosynthesis in Amycolatopsis mediterranei DSM5908: function of a halogenase and a haloperoxidase/perhydrolase

Glycopeptides are important clinical emergency antibiotics consisting of a glycosylated and chlorinated heptapeptide backbone. The understanding of the biosynthesis is crucial for development of new glycopeptides. With balhimycin as a model system, this work focuses on the investigation of the putative halogenase gene (bhaA) and the putative haloperoxidase/perhydrolase gene (bhp) of the balhimycin biosynthesis gene cluster. An in-frame deletion mutant in the haloperoxidase/perhydrolase gene bhp (OP696) did not produce balhimycin. Feeding experiments revealed that bhp is involved in the biosynthesis of beta-hydroxytyrosine, a precursor of balhimycin. A bhaA in-frame deletion mutant (PH4) accumulated glycosylated but nonchlorinated balhimycin variants. The mutants indicated that only the halogenase BhaA is required for chlorination of balhimycin. Nonglycosylated and/or nonhalogenated metabolites can serve as starting points for combinatorial approaches for novel glycopeptides.     

Über Kondensationen ungesättigter Verbindungen mit Diazomethan

Ohne Zusammenfassung     

Autoparametric quasiperiodic excitation

The dynamics of an autonomous conservative three degree of freedom system which exhibits autoparametric quasiperiodic excitation is investigated. The system is a generalization of a classical system known as the “particle in the plane”. The system exhibits a motion, the z=0 mode, whose stability is governed by a linear second order ODE with quasiperiodic coefficients. The behavior of the latter ODE is studied by using three different methods: numerical integration, harmonic balance and perturbation methods.