Die Struktur von HfAl

Zusammenfassung HfAl kristallisiert rhombisch (D ₂ ⁵ ) mit den Gitterkonstantena=10,81;b=3,24₉;c=4,27₂kX. E. Die Struktur, offensichtlich ein eigener Typ, wird ermittelt und diskutiert.Mit 1 Abbildungen     

Zur Kristallstruktur von CuGeO3

The crystal structure of CuGeO₃ (D _2h ⁵ -Pbmm) has been redetermined by means of 3-dimensional Fourier syntheses. The structure is built up by [CuO₄]- and [GeO₃]-chains (Einereinfachkette). The interatomic distances are found to be: Ge?O: 1,76₉ (2x) and 1,72₄ (2x) Å; Cu?O: 1,94₂ (4x) and 2,76₆ (2x) Å.     

Reaktionen des Diazomethans mitα,β-ungesättigten Aldehyden

Zusammenfassung Das Ausbleiben der Holzfarbreaktionen nach Vorbehandlung von Fichtenholz undBrauns Nativlignin durch Oxydation, katalytische Hydrierung und insbesondere nach Umsetzung mit Diazomethan wird an Hand von Modellsubstanzen [Zimtaldehyd und Methylconiferylaldehyd (3,4-Dimethoxyzimtaldehyd)] studiert. Aboxydation der Seitenkette, Hydrierung der Doppelbindung und Reaktion zu den entsprechenden 4-substituierten Pyrazolin-3-aldehyden verhindern deren Entstehen. Die Konstitution dieser Aldehyde wurde sichergestellt. Der Stickstoffgehalt von mit Diazomethan methyliertem Holz oder Nativlignin kann somit zumindest teilweise durch die Bildung von Pyrazolinen erklärt werden.Herrn Prof. Dr.A. Franke zum 80. Geburtstag gewidmet.     

Synthesis of periodic femtosecond pulse trains in the ultraviolet by phase-locked Raman sideband generation

We demonstrate a new technique for femtosecond-pulse generation that employs ultrafast modulation of a laser field phase by impulsively excited molecular rotational or vibrational motion with subsequent temporal compression. An ultrashort pump pulse at 800 nm performs impulsive excitation of a molecular gas in a hollow waveguide, and a weak delayed probe pulse at 400 nm is scattered on the temporal oscillations of its dielectric index. The resultant sinusoidal phase modulation of the probe pulse permits probe pulse temporal compression by use of both positively and negatively dispersive elements. The potential of this new method is demonstrated by the generation of a periodic train of 5.8-fs pulses at 400 nm with positive group-delay dispersion compensation.     

Regioselective Cleavage of Thioether Linkages in Microcystin Conjugates

Microcystins are cyanobacterial toxins that can be found in fresh and coastal waters during algal blooms. Microcystin contamination of water can cause severe poisoning of animals and humans. Quantification of these toxins in biological samples is complicated because a major proportion of microcystins is covalently linked to proteins through thioether bonds formed through a Michael‐type addition of cysteine residues of proteins to an N‐methyldehydroalanine residue in the microcystins. We investigated chemical methods that can be used to cleave such thioether bonds by means of an elimination reaction that leaves the microcystin backbone intact for subsequent analysis. The known reagent O‐mesitylenesulfonylhydroxylamine (MSH) led to regioselective thioether cleavage, but a large excess of reagent was needed, thus making purification challenging. An unexpected side reaction observed during the investigation of the base‐induced elimination inspired us to develop a new thioether‐cleavage methodology based on the addition of propargylamine as a nucleophile that can trap the elimination product. This methodology could be successfully applied to the quantitative cleavage of a microcystin‐LF–glutathione conjugate. The alkyne moiety introduced by this procedure offers the possibility for further reactions with azides by using click chemistry, which might be useful for the derivatization or isolation of microcystins.     

How relieving is public debt relief? Monetary and fiscal policies in a monetary union during a debt crisis

Central European Journal of Operations Research - We use a dynamic game model of a two-country monetary union to study the consequences of sovereign debt reliefs for a member country or bloc of...     

Kriechmessungen an Zementstein

Zusammenfassung Aus Kriechmessungen an Zementstein wurden mit Hilfe einer elektronischen Rechenanlage die Parameter der früher abgeleiteten Kriechgleichung für zwei Wasser/Zement-VerhÄltnisse bestimmt. Damit lÄßt sich die Aktivierungsenergie bestimmen. Für Zementstein mitW/Z = 0,3 bzw.W/Z = 0,65 findet man nach einer Belastungsdauer von 1000 StundenQ = 2,7 kcal/ Mol bzw. 2,3 kcal/Mol. Diese Werte stimmen gut mit den in der Literatur zu findenden Angaben überein. Die Verminderung der Aktivierungsenergie in Richtung der angreifenden Kraft betrÄgt für Zementstein mitW/Z = 0,3 bzw.W/Z = 0,65 ungefÄhr 1 kg^–1 bzw. 2kg^–1

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Summary The parameters in the equation for creep velocity as a function of time were calculated by means of a computer. The calculation is based on experiments on cement stone. The activation energy was determined. After applying a constant load for 1000 h the activation energy was found to beQ = 2.7 kcal/Mol andQ = 2.3 kcal/Mol in cement stone with a water/cement-ratio of 0.3 and 0.65 respectively. These values are in good agreement with the results of other papers. The activation energy in the direction of the external applied load is decreased by an amount of approximately 1 kg^–1 and 2 kg^–1 for cement stone with a water/cement-ratio of 0.3 and 0.65 respectively.

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Herr Prof. Dr. Dr.H. Rüsch förderte die Arbeit stets durch großes Interesse und durch interessante Anregungen. Der Deutschen Forschungsgemeinschaft danken wir für die Bereitstellung von Mitteln.