Nicht-lineare Elastizitätstheorie der Versetzungen und Eigenspannungen

Ohne Zusammenfassung Vorgelegt von J. Meixner Herrn Professor Dr. Dr. h. c. Richard Grammel zu seinem siebzigsten Geburtstag am 3. März 1959 gewidmet     

Measurement of the conditioned turbulence and temperature field of a premixed Bunsen burner by planar laser Rayleigh scattering and stereo particle image velocimetry

The turbulence and temperature field of Bunsen-type turbulent lean methane/air flames has been investigated using planar laser Rayleigh scattering (PLRS) and stereo particle image velocimetry (stereo PIV). Temporally averaged reaction progress variable plots have been computed from PLRS measurements in order to provide a basis with regards to the verification of computational fluid dynamics (CFD) models. Turbulence was characterised by stereo PIV in one plane for all three velocity components. Averaged velocity fields have been calculated, as well as Reynolds-decomposed fluctuation vector fields. Conditioned root mean square (RMS) values of the turbulent fluctuations in terms of unburnt and burnt gas could be determined by making use of the information gained from a threshold setting procedure in the PIV raw images. Furthermore, several length scales were measured indirectly from PIV vector plots. In this context, all integral length scales being accessible with stereo PIV were computed separately for the burnt and unburnt regions and were compared to each other. It could be observed that all integral length scales increased in the burnt zone. Additionally, the conditioned Taylor and Kolmogorov lengths have been extracted from the PIV field data, derived either from the zero-radius curvature of the correlation function or from common turbulence theory relations.     

Non-linear dynamic phenomena in the behaviour of a railway wheelset model

A dicone moving on a pair of cylindrical rails can be considered as a simplified model of a railway wheelset. Taking into account the non-linear friction laws of rolling contact, the equations of motion for this non-linear mechanical system result in a set of differential-algebraic equations. Previous simulations performed with the differential-algebraic solver DASSL, [2], and experiments, [7], indicated non-linear phenomena such as limit-cycles, bifurcations as well as chaotic behaviour. In this paper the non-linear phenomena are investigated in more detail with the aid of special in-house software and the path-following algorithm PATH [10]. We apply Poincaré sections and Poincaré maps to describe the structure of periodic, quasiperiodic and chaotic motions. The analyses show that part of the chaotic behaviour of the non-linear system can be fully understood as a non-linear iterative process. The resulting stretching and folding processes are illustrated by series of Poincaré sections.     

Water cavitation of hydrogels

Using the cavitation rheology (CR) technique developed in our labs, we show that fluids with negligible interfacial tensions with a surrounding material can be used to induce an elastic, cavitation instability in that material. We do this by changing the cavitation media from air, which was demonstrated to induce cavitation at the tip of a syringe needle in previous studies, to water, which has a negligible surface tension with the surrounding poly(vinyl alcohol) hydrogel material. In this case, the critical pressure in which this instability occurs can be directly related to the elastic modulus of the surrounding network and is shown to be nearly independent of length scale. This independence of size scale has important implications in the use of CR for the characterization of mechanical properties from molecular to macroscopic length scales. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1423–1427, 2010     

Drug–Membrane Interaction on Immobilized Liposome Chromatography Compared to Immobilized Artificial Membrane (IAM), Liposome/Water,and Octan‐1‐ol/Water Systems

The objective of this study was to investigate drug–membrane interaction by immobilized liposome chromatography (ILC; expressed as lipophilicity index log K_s) and the comparison with lipophilicity indices obtained by liposome/H₂O, octan‐1‐ol/H₂O, and immobilized artificial membrane (IAM) systems. A set of structurally diverse monofunctional compounds and drugs (nonsteroidal anti‐inflammatory drugs and β‐blockers) were selected in this study. This set of solutes consists of basic or acidic functionalities which are positively or negatively charged at physiological pH 7.4. No correlation was found between log K_s from ILC and lipophilicity indices from any of the other membrane model systems for the whole set of compounds. For structurally related compounds, significant correlations could be established between log K_s from ILC and lipophilicity indices from IAM chromatography and octan‐1‐ol/H₂O. However, ILC and liposome/H₂O systems only yield parallel partitioning information for structurally related large molecules. For hydrophilic compounds, the balance between electrostatic and hydrophobic interactions dominating drug partitioning is different in these two systems.     

First emission studies of Tc2X8(2-) systems (X = Cl, Br)

The emission spectra of the solids [n-Bu(4)N](2)Tc(2)X(8) (X = Cl, Br) have been investigated at room temperature and 77 K. In each case, the emission originates in the (1)δ-δ* excited state, as with the rhenium homologues, but has a shorter lifetime.     

Variation of the ultrafast fluorescence quenching in 2,6-sulfanyl-core-substituted naphthalenediimides by electron transfer

The ultrafast fluorescence quenching of 2,6-sulfanyl-core-substituted naphthalenediimides was investigated by transient spectroscopy. We find a strong dependence of the relaxation on the chemical structure of the substituent. Direct linking of an aryl rest to the sulfur atom leads to a strong red shift of the fluorescence in 1 ps and the disappearance of the emission in 5-7 ps depending on the polarity and viscosity of the solvent. This complex behavior is interpreted with the help of quantum chemical calculations. The calculations suggest that the initial relaxation corresponds to a planarization of the substituents and an associated partial electron transfer. This is followed by a twisting of the phenylsulfanyl substituents out of the molecular plane that allows a complete localization of the electron-donating orbital on the aryl group. Finally the back transfer happens in another 5-7 ps. For an additional methylene spacer group between the sulfur and the aryl, this sequence of relaxation steps is not possible and a simple exponential decay, slower by about 1 order of magnitude, is found.     

A possible origin of room temperature ferromagnetism in Indium-Tin oxide thin film: Surface spin polarization and ferromagnetism

Room temperature ferromagnetism in both transition-metals doped and undoped semiconductor thin films and nanostructures challenges our understanding of the magnetism in solids. In this report, we performed the magnetic measurement and Andreev reflection spectroscopy study on undoped Indium-Tin oxide (ITO) thin films and bulk samples. The magnetic measurement results of thin films show that the total magnetization/cm² is thickness independent. Prominent ferromagnetism signal was also discovered in bulk samples. Spin polarized electron transports were probed on ITO thin film/superconductor interface and bulk samples surface/superconductor interface. Based on the magnetic measurement results and spin polarization measurement data, we propose that the ferromagnetism in this material originates from the surface spin polarization and this surface polarization may also explain the room temperature ferromagnetism discovered in other undoped oxide semiconductor thin films and nanostructures.