ORSAT and modifications of SEFT and APT

Up to now, three subspectra are usually needed for the complete assignment of all signals in 13C spectrum: two DEPT spectra (phi = 90 degrees and phi = 135 degrees) and a proton decoupled spectrum. In this paper, we present a method in which a complete assignment becomes possible with merely two spectra. For this purpose, a new pulse sequence (ORSAT) has been elaborated by using off-resonance irradiation. The method described here is a further development of SEFT and APT. The second required spectrum is a DEPT (phi = 135 degrees). Signal assignment of cholesteryl acetate is demonstrated as an example. 13C routine spectroscopy can be significantly accelerated by applying this method.     

Trace analysis of bromate and bromide with ion chromatography on coated reversed phase materials

 The ion-chromatographic method for trace analysis of bromate and bromide presented in this paper is based on coating of reversed phase (RP) material with an ionogenic agent, tetrakisdecylammonium bromide, to obtain a pseudo ion-exchange column. The analysis is carried out with usual HPLC pump and UV-detection near 200 nm. Some commercially available RP materials were tested for the coating procedure. The differences between the reversed phases are not significant. All HETP values are calculated between 0.02 and 0.14 mm. The calibration, the sensitivity of the method and the long-time stability of the coated column were tested with one selected RP material. It is shown that the simultaneous trace analysis of bromate and bromide in surface and drinking waters with chloride concentrations up to 50 mg/L is possible without any clean-up on Ag precolumns. A comparison of performance data with a determination method for bromate and bromide employing a commercially available equipment demonstrates the efficiency of the new technique. Received: 23 February 1996/Received: 10 May 1996/Accepted: 14 May 1996     

Liquid crystalline side group polymers with azo-chromophores and fluorinated tails of varying length

A series of side group liquid crystalline polymethacrylates with 4'-(1H,1H-perfluoroalkoxy)-azobenzene mesogenic units was synthesized and characterized by differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction methods depending on the tail length. The phase behaviour is discussed as a function of the length of the tail groups. Very high clearing temperatures up to 290°C were observed for the polymers with long tail groups.     

Zur Lumineszenz des Zinkoxyds

The temperature dependance of efficiency and decay of the ultraviolet and green luminescence bands at UV- and cathode ray-excitation is investigated. In addition to earlier results the Riehl-effect is only observed when excited by cathode rays. The UV-band decays hyperbolically at all temperatures while the decay of the green band depends on kind and intensity of the excitation as well as on temperature. The results can be interpreted by considering the increasing number of electrons in the conduction band under different kinds of excitation and the variation of conductivity with temperature. Furthermore, the glow curves of various ZnO-samples (untreated and annealed in reducing atmosphere) show one or two peaks respectively, thus revealing two trap depths. As the light sum increases with the efficiency it is assumed that by reduction both activators and traps are created. The occurrence of thermoluminescence with many conduction electrons being present leads to the assumption of hole traps.     

The contraction number of a multigrid method for solving the Poisson equation

Summary The treatment of a multigrid method in the framework of numerical analysis elucidates that regularity of the solution is not necessary for the convergence of the multigrid algorithm but only for fast convergence. For the linear equations which arise from the discretization of the Poisson equation, a convergence factor 0,5 is established independent of the shape of the domain and of the regularity of the solution.Dedicated to Professor Dr.Dr.h.c. Lothar Collatz on the occasion of his 70 th birthday