Inhalt eines Gefäßes in verschiedenen Abständen vom Erdmittelpunkt

Zeitschrift für Physik A Hadrons and nuclei -     

Quiver representations of maximal rank type and an application to representations of a quiver with three vertices

We introduce the notion of ‘maximal rank type’ forrepresentations of quivers, which requires certain collectionsof maps involved in the representation to be of maximal rank.We show that real root representations of quivers are of maximalrank type. By using the maximal rank type property and universalextension functors we construct all real root representationsof a particular wild quiver with three vertices. From this constructionit follows that real root representations of this quiver aretree modules. Moreover, formulae given by Ringel can be appliedto compute the dimension of the endomorphism ring of a givenreal root representation.     

Ein Beitrag zur Frage der Formgebung räumlich tragender Tonnenschalen

Ohne Zusammenfassung     

Effect of urea on analyte complexation by 2,6‐dimethyl‐β‐CD in peptide enantioseparations by CE

The aim of the present study was the investigation of the effect of urea on analyte complexation in CD‐mediated separations of peptide enantiomers by CE in the pH range of about 2–5. pH‐independent complexation and mobility parameters in the absence and presence of 2 M urea were obtained by three‐dimensional, non‐linear curve fitting of the effective analyte mobility as a function of pH and heptakis‐(2,6‐di‐O‐methyl)‐β‐CD concentration. Urea led to decreased binding strength of the CD towards the protonated and neutral analyte enantiomers as well as to decreased mobilities of the free analytes. In contrast, mobilities of the fully protonated enantiomer–CD complexes as well as the pK_a values of the free and complexed analytes increased. The effect of urea on separation efficiency varied with pH and CD concentration. In the case of Ala‐Tyr and Ala‐Phe, separations improved in the presence of urea at pH 2.2. In contrast, separations were impaired by urea at pH 3.8 and low concentrations of the CD. Decreased separation efficiency was noted for Asp‐PheOMe and Glu‐PheNH₂ at low CD concentrations when urea was added but separations improved at higher CD concentrations over the entire pH range studied. The effect of urea on analyte complexation appeared to be primarily non‐stereoselective. Furthermore, the pH‐dependent reversal of the enantiomer migration order observed for Ala‐Tyr and Ala‐Phe can be rationalized by the complexation and mobility parameters.     

Vapor Pressure Determination by Pressure DSC

A new pressure DSC module (Mettler DSC27HP) and its abilities for vapor pressure determination in the range of subambient pressure to 7 MPa are presented. To compare the new to an established method, vapor pressures of caffeine, naphthalene and o-phenacetin have been determined both by pressure DSC and the Knudsen effusion cell method. These results, including the derived heats of evaporation and heats of sublimation, are compared to literature values. This revised version was published online in July 2006 with corrections to the Cover Date.     

1-Nitratoethyl-5-nitriminotetrazole derivatives - Shaping future high explosives

1-(2-Nitratoethyl)-5-nitriminotetrazole (2) was formed by the reaction of 1-(2-hydroxyethyl-5-aminotetrazole (1) and 100% HNO₃. Compound 1 was obtained by alkylation of 5-amino-1H-tetrazole. Next to the known byproduct 1-(2-hydroxyethyl)-5-nitriminotetrazole (3), a second one, 1-(2-nitratoethyl)-5-aminotetrazolium nitrate (4) was obtained and fully characterized. Nitrogen-rich salts such as the ammonium (5), hydroxylammonium (6), guanidinium (7), aminoguanidinium (8), diaminoguanidinium (9) and triaminoguanidinium (10) 1-(2-nitratoethyl)-5-nitriminotetrazolate were prepared by deprotonation or metathesis reactions. The reaction of 2 and diaminourea yielded 1-(2-nitratoethyl)-5-aminotetrazole (11). Compounds 4-11 were fully characterized by single crystal X-ray diffraction, vibrational spectroscopy (IR and Raman), multinuclear NMR spectroscopy, elemental analysis and DSC measurements. The heats of formation of 5-10 were calculated by the atomization method based on CBS-4M enthalpies. Regarding the possible application of these compounds as energetic materials or high explosives, several detonation parameters such as the detonation pressure, velocity, energy and temperature were computed using the EXPLO5 code and the X-ray densities as well as the computed heats of formation. In addition the sensitivities towards impact, friction and electrical discharge were tested using the BAM drophammer, a friction tester as well as a small scale electrical discharge device.