Ein genaues und schnelles Verfahren zur kombinierten direkten Bestimmung der Oxydationsstufe des Vanadins und des Vanadingehalts von Metall-Vanadin-Sauerstoffverbindungen

Zusammenfassung Es wird ein Verfahren beschrieben, das es gestattet, in Metall- Vanadin-Sauerstoffverbindungen in einer Probe hintereinander die Oxydationsstufe des Vanadins und den Vanadingehalt auf maßanalytischem Wege mit großer Genauigkeit zu bestimmen. Zur Ermittlung der Oxydationsstufe wird mit einer bekannten Menge KMnO₄-Lösung oxydierend gelöst und mit FeSO₄-Lösung bis zum Vanadin(IV) zurücktitriert. Als Indicator wird Natrium-N-methyldiphenylamin-p-sulfonat verwendet. Anschließend wird mit KMnO₄ zum Vanadin(V) oxydiert, der KMnO₄-Überschuß mit Nitrit entfernt, das nicht umgesetzte Nitrit mit Harnstoff zerstört und der Vanadingehalt durch erneute Titration mit FeSO₄-Lösung bestimmt.     

Über Parallelstrukturen

Ohne ZusammenfassungTeil einer von der Naturwissenschaftlich-Philosophischen Fakultät der Technischen Hochschule Braunschweig angenommenen Habilitationsschrift.Teil I, Math. Z.76, 85–102, Teil II, Math. Z.76, 155–163, Teil III, Math. Z.76, 240–256 (1961); im folgenden hier mit I, II bzw. III zitiert.     

Aided self-assembly of porphyrin nanoaggregates into ring-shaped architectures

The formation of micrometer-sized, highly ordered porphyrin rings on surfaces has been investigated. The porphyrin-based nanoarchitectures are formed by deposition from evaporating solutions through a surface dewetting process which can be tuned by variations in the substitution pattern of the molecules used, the coating of the surface and the conditions under which the evaporation takes place. Control over the combined self-assembly and surface dewetting results in nanorings possessing a defined internal architecture. The ordering of the molecules within the rings has been studied by a variety of microscopy techniques (TEM, AFM, fluorescence microscopy) and the exact ordering of the porphyrins within the rings has been quantified.     

Electronic and photophysical properties of a novel phenol bound dinuclear ruthenium complex: evidence for a luminescent mixed valence state

A novel dinuclear ruthenium(II) complex bridged by dianionic bridge 3-(2-phenol)-5-(pyridin-2-yl)-1,2,4-triazole in which the ruthenium metal atoms are bound through N,N coordination to the pyridine and triazole and O,N coordination to the triazole and phenolate is described. The electrochemical, spectroscopic and photophysical behaviour of the dimer is compared with its associated N,N- and O,N-coordinated mononuclear complexes. The mixed valence complex was prepared electrochemically and a weak inter-valence charge transfer transition is observed which from Hush theory provides an electronic coupling matrix element of 666 cm(-1), suggesting the complex is weakly coupled and valence trapped. In its native state the dinuclear compound is essentially non-emissive but upon the oxidation of the O,N moiety luminescence from the complex is reversibly switched on at 0.3 V and reversibly switched off by application of 1.3 or 0 V. To our knowledge this is the first report of a luminescent mixed valence ruthenium complex.     

Optimization of rod antennas of mobile phones

Two types of rod antennas of mobile phones are optimized so that the radiated energy absorbed by the head or body of the user is reduced and the radiation intensity to other areas especially to the receiver is increased. The mathematical modelling of this problem leads to an infinite dimensional bicriterial optimization problem. It is shown that this optimization problem and a discretized version of this problem are solvable. The relationship between the infinite and finite dimensional optimization problem is investigated. Numerical results are presented for mobile phones working with the GSM standards 900 and 1800.     

Methodological aspects of an adaptive multidirectional pattern search to optimize speech perception using three hearing-aid algorithms

In this study we investigated the reliability and convergence characteristics of an adaptive multidirectional pattern search procedure, relative to a nonadaptive multidirectional pattern search procedure. The procedure was designed to optimize three speech-processing strategies. These comprise noise reduction, spectral enhancement, and spectral lift. The search is based on a paired-comparison paradigm, in which subjects evaluated the listening comfort of speech-in-noise fragments. The procedural and nonprocedural factors that influence the reliability and convergence of the procedure are studied using various test conditions. The test conditions combine different tests, initial settings, background noise types, and step size configurations. Seven normal hearing subjects participated in this study. The results indicate that the reliability of the optimization strategy may benefit from the use of an adaptive step size. Decreasing the step size increases accuracy, while increasing the step size can be beneficial to create clear perceptual differences in the comparisons. The reliability also depends on starting point, stop criterion, step size constraints, background noise, algorithms used, as well as the presence of drifting cues and suboptimal settings. There appears to be a trade-off between reliability and convergence, i.e., when the step size is enlarged the reliability improves, but the convergence deteriorates.     

Enhancement of the superconducting transition temperature of MgB2 by a strain-induced bond-stretching mode softening

We report a systematic increase of the superconducting transition temperature T(c) with a biaxial tensile strain in MgB2 films to well beyond the bulk value. The tensile strain increases with the MgB2 film thickness, caused primarily by the coalescence of initially nucleated discrete islands (the Volmer-Weber growth mode.) The T(c) increase was observed in epitaxial films on SiC and sapphire substrates, although the T(c) values were different for the two substrates due to different lattice parameters and thermal expansion coefficients. We identified, by first-principles calculations, the underlying mechanism for the T(c) increase to be the softening of the bond-stretching E(2g) phonon mode, and we confirmed this conclusion by Raman scattering measurements. The result suggests that the E(2g) phonon softening is a possible avenue to achieve even higher T(c) in MgB2-related material systems.     

Sorption isotherm measurements by NMR

An experimental setup is described for the automated recording of sorption isotherms by NMR experiments at precisely defined levels of relative humidity (RH). Implementation is demonstrated for a cotton fabric; Bloch decays. T1 and T2* relaxation times were measured at predefined steps of increasing and decreasing relative humidities (RHs) so that a complete isotherm of NMR properties was obtained. Bloch decays were analyzed by fitting to relaxation functions consisting or a slow- and a fast-relaxing component. The fraction of slow-relaxing component was greater than the fraction of sorbed moisture determined from gravimetric sorption data. The excess slow-relaxing component was attributed to plasticized segments of the formerly rigid cellulose matrix. T1 and T2* sorption isotherms exhibit hysteresis similar to gravimetric sorption isotherms. However, correlating RH to moisture content (MC) reveals that both relaxation constants depend only on MC, and not on the history of moisture exposure.     

Enantioselective transport by a steroidal guanidinium receptor

The cationic steroidal receptors 9 and 11 have been synthesized from cholic acid 3. Receptor 9 extracts N-acetyl-alpha-amino acids from aqueous media into chloroform with enantioselectivities (L:D) of 7-10:1. The lipophilic variant 11 has been employed for the enantioselective transport of N-acetylphenylalanine, a) through dichloromethane (DCM) and dichloroethane (DCE) bulk liquid membranes (U-tube apparatus), and b) through 2.5% (v/v) octanol/hexane via hollow fibre membrane contactors. Significant enantioselectivities and multiple turnovers were observed for both types of apparatus.