Ultrasound-assisted extraction in the fractionation analysis of gravitation dust sediments

Ultrasound-assisted extraction is frequently used to prepare analytical samples and is considered an alternative to conventional extraction techniques. Extraction procedures are used in the fractionation analysis for the isolation of various element species. The recoveries of elements in the ultrasonic extracts were tested by comparing these results with those of conventional extraction procedures. Contents of Cu, Pb, and Zn in extracts obtained by both the conventional and the ultrasound-assisted extraction were determined by flame atomic absorption spectrometry. The optimal conditions for the ultrasound-assisted extraction (sonication power = 90%, depth of ultrasonic probe = 4 cm) were determined, and the extraction time was shortened to 6 min (using EDTA) and to 5 min using HNO₃ extraction reagent.     

Über die photometrische Bestimmung des Aluminiumgehaltes von legierten Stählen mit 8-Hydroxychinolin (Oxin)

The known method applying an alkaline separation [2, 5] has been revised. The procedure is simple, rapid and exact. Alloying elements, even in high concentrations, do not interfere. 0.005–1.5% of aluminium can be determined.     

Angular limits of the integrals of the Cauchy type

Integrals of the Cauchy type extended over the boundary A of a general compact set A in the complex plane are investigated. Necessary and sufficient conditions on A are established guaranteeing the existence of angular limits of these integrals at a fixed zA for all densities satisfying a Hölder-type condition at z     

Molecular beam epitaxy (MBE) growth and structural properties of GaN and AlN on 3C-SiC(0 0 1) substrates

AlN and GaN was deposited by molecular beam epitaxy (MBE) on 3C-SiC(0 0 1) substrates on low-temperature (LT) GaN and AlN buffer layers. It is shown that not only GaN but also epitaxial AlN can be stabilized in the metastable zincblende phase. The zincblende AlN is only obtained on a zincblende LT-GaN buffer layer; on the other hand, AlN crystallizes in the wurtzite phase if it is grown directly on a 3C-SiC(0 0 1) substrate or on a LT-AlN buffer layer. The structural properties of the layers and in particular the orientation relationship of the wurtzite AlN on the 3C-SiC(0 0 1) were analyzed by conventional and high-resolution transmission electron microscopy.     

Quantitative characterization of AlAs/GaAs interfaces by high-resolution transmission electron microscopy along the 〈100〉 and the 〈110〉 projection

The interface microstructure of AlAs/GaAs quantum wells grown by molecular beam epitaxy (MBE) was investigated by transmission electron microscopy (TEM). High-resolution transmission electron microscopy (HRTEM) yields information about the width of the chemical transition between the binary components and about the lateral step distances along the interface. The chemical composition is quantitatively determined by the application of a pattern recognition procedure based on the Fourier transformation of image unit cells. Along the 100 zone axis the composition across the interfaces is obtained with a precision of ±10 atomic percent and with a spatial resolution of 0.28 nm. Despite a lower chemical sensitivity a quantitative chemical analysis was also carried out for images along the 110 projection.     

[Mg3Cl5(Et2O)6]+: Darstellung,Strukturbestimmung und ab-initio-Untersuchungen

[Mg₃Cl₅(Et₂O)₆]⁺: Synthesis, Structure, and Ab-Initio Calculations The cation [Mg₃Cl₅(Et₂O)₆]⁺ of a chlorogallat has been prepared in a reaction of Ga₂Cl₄ with MgCp and was characterized by a X-ray single-crystal structure analysis. For understanding of the conditions of formation of neutral and charged magnesium chlorids and of the processes in the complex reaction system ab-initio calculations were performed.     

Analysis of Fatty Acid, and Lipoprotein, Metabolism by GC and HPLC: Effect of Low-Density Lipoprotein Apheresis

 Blood samples from 5 hyperlipidemic patients on chronic treatment with low-density lipoprotein (LDL) – apheresis were analysed for lipids and fatty acids in serum, lipoprotein fractions and erythrocyte membrane by capillary gas chromatography (GC), reversed-phase high-performance liquid chromatography (LC), spectrofluorometry and spectrophotometry. LDL-apheresis has been associated with significant changes of fatty acids metabolism in relation to triglyceride-rich lipoproteins. Oleic acid may exert its hypotriglyceridemic effect via VLDL, IDL, LDL and HDL fractions. Polyunsaturated fatty acids, associated with triglyceride metabolism via IDL or VLDL, are linoleic, gamma-linolenic and docosahexaenoic fatty acids. Received November 25, 1999. Revision September 5, 2000.     

SCHWEFELVERBINDUNGEN DES ERDÖLS XVI.1 DIBENZOTHIOPHENE MIT EINEM UNVERZWEIGTEN C1[sbnd]C5-ALKYLREST

Abstract

The preparation of all position isomeres of dibenzothiophenes with a linear C₁[sbnd]C₅-sidechain and of the corresponding 5,5-dioxides is described. ¹H-NMR-data and GC-purities are given.

Die Darstellung von allen stellungsisomeren Dibenzothiophenen mit einer unverzweigten C₁[sbnd]C₅-Seitenkette und der zugehörigen 5,5-Dioxide wird beschrieben. ¹H-NMR-Daten und GC-Reinheiten werden gebracht.     

Kinetic Modeling as a Tool to Understand and Improve the Nitroxide Mediated Polymerization of Styrene

Kinetic modeling is used to obtain insight in the complex interplay between reaction rates and obtained polymer properties in the SG1 and the TEMPO mediated bulk polymerization of styrene at 396 K. The increase of the viscosity during NMP is accounted for. At higher targeted chain lengths, chain transfer to dimer and transfer from nitroxide to dimer are shown to cause the experimentally observed reduced control over the average polymer properties and to result in a clear fronting of the polymer chain length distribution. The potential of kinetic modeling to design tailor‐made synthesis strategies is illustrated. Simulations indicate that careful control of the polymerization conditions allows to obtain an important improvement of the polymer properties. The approach is also applicable for NMP mediated by other alkoxyamines/nitroxides and allows to expand the application range of NMP for styrene polymerization in particular to synthesize complex polymer architectures by assembly of functionalized polymers.