Electro-Mechanochemical Atom Transfer Radical Cyclizations using Piezoelectric BaTiO3

The formation and regeneration of active Cu^I species is a fundamental mechanistic step in copper-catalyzed atom transfer radical cyclizations (ATRC). Typically, the presence of the catalytically active Cu^I species in the reaction mixture is secured by using high Cu^I catalyst loadings or the addition of complementary reducing agents. In this study it is demonstrated how the piezoelectric properties of barium titanate (BaTiO₃) can be harnessed by mechanical ball milling to induce electrical polarization in the strained piezomaterial. This strategy enables the conversion of mechanical energy into electrical energy, leading to the reduction of a Cu^II precatalyst into the active Cu^I species in copper-catalyzed mechanochemical solvent-free ATRC reactions.     

Two-dimensional asymptotic expansions for large deviations of spherically distributed random vectors if the dominating point degenerates asymptotically

A geometric approach to asymptotic expansions for large-deviation probabilities, developed for the Gaussian law by Breitung and Richter [J. Multivariate Anal.,58, 1–20 (1996)], will be extended in the present paper to the class of spherical measures by utilizing their common geometric properties. This approach consists of rewriting the probabilities under consideration as large parameter values of the Laplace transform of a suitably defined function, expanding this function in a power series, and then applying Watson’s lemma. A geometric representation of the Laplace transform allows one to combine the global and local properties of both the underlying measure and the large-deviation domain. A special new type of difficulty is to be dealt with because the so-called dominating points of the large-deviation domain degenerate asymptotically. As is shown in Richter and Schumacher (in print), the typical statistical applications of large-deviation theory lead to such situations. In the present paper, consideration is restricted to a certain two-dimensional domain of large-deviations having asymptotically degenerating dominating points. The key assumption is a parametrized expansion for the inverse $\bar g^{ - 1} $ of the negative logarithm of the density-generating function of the two-dimensional spherical law under consideration.     

On the Diameter of Plane Curves

Recently, differential geometric properties of embedded projective varieties have gained increasing interest. In this note, we consider plane algebraic curves equipped with the Fubini--Study metric from₂ () and give an estimate for the diameter in terms of the degree, initiated in a paper by F. A. Bogomolov.     

The angular dependence of flux,mean energy and speed ratio for D2 molecules desorbing from a Ni(111) surface

Experimental data are presented for the angular dependence of the relative flux, the mean energy and the speed ratio of deuterium molecules desorbing from a Ni(111) crystal surface at a surface temperature of T_s = 1143 K and at sulphur coverages ranging between 30% and less than 2% of a monolayer.The angular flux distribution is sharply peaked in the forward direction (cos^dθwith 3 ? d ? 5) and the mean energy 〈E〉 of the desorbate depends strongly on the desorption angle θ. For normal desorption $\text{(θ = 0°)}\text{〈E〉}\text{2k}$ is about 700 K higher than T_s and for glancing angles (θ = 80°) it decreases to about 400 K below T_s The results obtained on sulphur free and sulphur covered Ni(111) surfaces are compared with our former data on polycrystalline nickel. The main differences in the kinetic features can be ascribed to the surface roughness. Accordingly, the angular distributions of flux, mean energy, and speed ratio, which deviate strongly from the Knudson and Maxwellian law, do not seem to depend considerably on sulphur coverage and surface structure. A qualitative explanation for these deviations is presented using the principle of detailed balancing.     

Minimale und maximale Tripelerzeugende und eine Bemerkung zur Tripelbarkeit

Ohne Zusammenfassung     

Bestimmung von Cadmium durch flammenlose Atom-Absorptions-Spektralphotometrie

Zusammenfassung Der Einfluß der Carbidbeschichtung von Graphitrohren auf die Bestimmung von Cd mit der flammenlosen AAS wurde systematisch untersucht. Dazu wurden die Graphitrohröfen mit Zr-, Nb-, Ta-, Mo- und W-Salzlösungen imprägniert, getrocknet und anschließend zur Einleitung der Carbidbildung bei 2600° C geglüht. Es zeigte sich, daß die Oberflächenbehandlung mit Carbidbildnern insgesamt die Lebensdauer des Graphitrohres in Anwesenheit starker Oxidationsmittel erhöht. Außerdem ließen sich höhere Matrix-Zersetzungstemperaturen ohne Cadmium-Verluste erreichen. Die Beschichtung mit Nb-, Ta- und W-Carbid erbrachte auch eine erhöhte Reproduzierbarkeit. Die günstigsten Ergebnisse lieferte die Ta-Beschichtung mit einer Zersetzungstemperatur von 450° C bei Verwendung von N₂-Schutzgas, die bei Anwendung starker Oxidationsmittel auf 600° C gesteigert werden konnte. Damit erlaubt die TaBeschichtung die direkte Cd-Bestimmung selbst in Gegenwart geringer organischer Matrixanteile. Gleichzeitig waren Reproduzierbarkeit und Empfindlichkeit gegenüber dem unbeschichteten Rohr deutlich verbessert.

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Determination of cadmium by flameless atomic-absorption spectroscopy

Summary The influence of coating of graphite furnace tubes with carbide forming metals on the determination of Cd by flameless AAS has been investigated systematically. The graphite furnace tubes have been impregnated with Zr, Nb, Ta, Mo or W salt solutions, dried and subsequently annealed up to 2,600° C to initiate carbide formation. It has been found that the surface treatment with carbide forming metals increased the lifetime of the graphite tube in the presence of strongly oxidizing agents. Furthermore, higher decomposition temperatures could be applied without Cd losses and coating with Nb. Ta and W carbide led to higher reproducibility. Best results have been obtained by coating with Ta allowing a decomposition temperature of about 450° C for N₂ as inert gas, that could even be enhanced to 600° C by application of strongly oxidizing agents. Thereby Ta coating makes possible direct Cd determination even in the presence of small organic admixtures to the matrix. At the same time reproducibility and sensitivity were improved as against the uncoated tube.

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Herrn Prof. Dr. H. Weisz zum 60. Geburtstag gewidmet     

Recovery of potato apices after several years of storage in liquid nitrogen

A method for the systematic cryopreservation of potato apices was developed by the Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH (DSMZ) and the Institute for Crop and Grassland Science of the Federal Agricultural Research Centre (FAL, Braunschweig). Designed specifically for routine use in genebanks, this method uses a very simple ultra-rapid freezing approach and was applied to a wide range of varieties within the Federal Centre for Breeding Research on Cultivated Plants (BAZ, Quedlinburg) Potato Collection. After several years of storage in liquid nitrogen, shoot tips from a random sample of 51 varieties were thawed and the survival and shoot regeneration percentages compared to those measured immediately after freezing. There were no major changes in either survival or recovery of frozen apices. Data presented are not the outcome of a systematic experiment but from that accumulated during our work from 1992 to 1999.