Chelate von β-dicarbonylverbindungen und ihren derivaten : Teil L. Die extraktionsphotometrische bestimmung von zink und wismut mit thiodibenzoylmethan

Thiodibenzoylmethane is suitable for the extraction-photometric determination of traces of zinc and bismuth. The method is satisfactory in glycine-buffered solutions at pH 12.6 Interfering metal ions are masked by diethanolamine-dithiocarbamate in the determination of zinc and by cyanide in the case of bismuth; many foreign ions can be tolerated in more than 100-fold amounts     

Formation of hollow atoms at metal- and insulator surfaces

Received: 27 March 1998/Accepted: 23 October 1998     

Zur Übertragung des Alternativsatzes der Fredholmschen Theorie auf algebraische Integralgleichungen

Ohne ZusammenfassungHerrnAlexander Ostrowski zum 60. Geburtstag gewidmetDie vom erstgenannten Verfasser aufgestellte, in der vorliegenden Note dargestellte Vermutung des Alternativsatzes wurde in dauernder Gemeinschaftsarbeit zwischen beiden am Institut fÜr Mathematik der T. H. Berlin-Charlottenburg tätigen Verfassern in dem hier gegebenen Umfange bewiesen.     

Charge-transfer complexation as a general phenomenon in the copigmentation of anthocyanins

Color intensification of anthocyanin solutions in the presence of natural polyphenols (copigmentation) is re-interpreted in terms of charge transfer from the copigment to the anthocyanin. Flavylium cations are shown to be excellent electron acceptors (E(red) approximately -0.3 V vs SCE). It is also demonstrated, for a large series of anthocyanin-copigment pairs, that the standard Gibbs free energy of complex formation decreases linearly with EA(Anthoc) - IP(Cop), the difference between the electron affinity of the anthocyanin, EA(Anthoc), and the ionization potential of the copigment, IP(Cop). Based on this correlation, copigmentation strengths of potential candidates for copigments can be predicted.     

Mathematische Begründung der Scheibentheorie (zweidimensionale Elastizitätstheorie)

Ohne Zusammenfassung Vorgelegt von Eli Sternberg     

Zur überführung beliebiger positiver Matrizen in stochastische und doppelt-stochastische Matrizen

Ohne Zusammenfassung     

Elastoacoustic model with uncertain mechanical properties for ultrasonic wave velocity prediction: application to cortical bone evaluation

The axial transmission technique can measure the longitudinal wave velocity of an immersed solid. An elementary model of the technique is developed with a set of source and receivers placed in a semi-infinite fluid coupled at a plane interface with a semi-infinite solid. The acoustic fluid is homogeneous. The solid is homogeneous, isotropic, and linearly elastic. The work is focused on the prediction of the measured velocity (apparent velocity) when the solid is considered to have random material properties. The probability density functions of the random variables modeling each mechanical parameter of the solid are derived following the maximum entropy principle. Specific attention is paid to the modeling of Poisson's ratio so that the second-order moments of the velocities remain finite. The stochastic solver is based on a Monte Carlo numerical simulation and uses an exact semianalytic expression of the acoustic response derived with the Cagniard-de Hoop method. Results are presented for a solid with the material properties of cortical bone. The estimated mean values and confidence regions of the apparent velocity are presented for various dispersion levels of the random parameters. A sensibility analysis with respect to the source and receivers locations is presented.     

Lyapunov exponents of partially hyperbolic volume-preserving maps with 2-dimensional center bundle

We consider the set of partially hyperbolic symplectic diffeomorphisms which are accessible, have 2-dimensional center bundle and satisfy some pinching and bunching conditions. In this set, we prove that the non-uniformly hyperbolic maps are $C^r$ open and there exists a $C^r$ open and dense subset of continuity points for the center Lyapunov exponents. We also generalize these results to volume-preserving systems.     

Microbiological control and antibacterial action of a propolis-containing mouthwash and control of dental plaque in humans

Propolis is a bee product with several biological properties. This study aimed at investigating a propolis-containing mouthwash, its organoleptic properties, microbial contamination and its antibacterial action in vitro. This mouthwash was assessed in vivo to control dental plaque in humans. The presence of microorganisms was analyzed and the minimum inhibitory concentration against Streptococcus mutans was determined. A comparative study was done in vivo using propolis, chlorhexidine, and propolis plus chlorhexidine in lower concentrations for 14 days. Dental plaque was analyzed by the Patient Hygiene Performance (PHP) index. The odontological product was yellow, cloudy, free of microbial contamination, and exerted an inhibitory action in vitro. Individuals who used a propolis-containing mouthwash for 14 consecutive days in combination or not to chlorhexidine showed a similar PHP index to chlorhexidine alone. The product exerted an antibacterial action in vitro and in vivo, exhibiting a positive action in the control of dental plaque.