Local Entropy Conditions in Transonic Potential Flow Problems

The transonic potential flow problem is handled as a variational problem over a closed convex set which is given by a bound for the gas velocity and by a local entropy condition. It can be shown that the minimum problem has a solution though the functional need not be convex and the given set is not compact. Furthermore, the convergence of an approximation method (KATCHANOV'S method) for the solution to the corresponding variational inequality is proved.     

Neue Pyridiniumchlorometallatverbindungen der Seltenerdelemente

Summary Reaction of the rare earth chlorides with pyridinium chloride in tetrahydrofuran (THF) under anhydrous conditions gave nearly insoluble precipitates of the composition (pyH)₃ RECl₆·THF (RE=La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y, Er, Tm, Yb, and Lu). They were characterized by chemical analysis and IR spectroscopy; decompositionin vacuo was studied, yielding the hithero unknown complexes (pyH)₃ RECl₆ (RE=La, Ce, Pr, Sm, Tb, Ho, Y, Tm, and Lu).

     

Preparation of micro- and nanopatterns of polymer chains grafted onto flexible polymer substrates

In this work a simple novel method for preparing micro- and nanoscale patterns of polymer chains grafted onto flexible polymer substrates is described. A combination of the two techniques of radiation grafting and "grafting-from" has been made. This combination makes it possible to prepare grafted structures having micro- or nanoscale lateral dimensions that are determined by the electron beam or X-ray irradiation patterns used. The height of the grafted features can be controlled by the irradiation dose or such grafting reaction conditions as time, temperature, or monomer concentration. Our first results for nanopatterned samples demonstrate resolution comparable to those of other polymer-based lithography processes.     

Rhodium and palladium β-diketonate determination with on-line supercritical fluid extraction-high performance liquid chromatography via solid phase extraction

 An on-line system of supercritical fluid extraction (SFE) and high performance liquid chromatography (HPLC) via solid phase extraction (SPE) is described for the determination of palladium and rhodium 2,2,6,6-tetramethyl-3,5-heptanedione-(thd) as well as rhodium-acetylacetonate-(acac) and benzylacetonate-(bzac) chelates. The chelates were extracted with supercritical CO₂ from sand and humic acid, concentrated on SPE cartridges and analysed with HPLC. Two cartridge materials were tested and compared to off-line trapping. The percentage of the breakthrough and cartridge retained material were measured in liquid dichloromethane. The SFE conditions could be optimized to separate metal chelates during the extraction. The supercritical fluid (SF) behaviour of different ligands on rhodium were investigated. Received: 19 July 1996/Revised: 11 December 1996/Accepted: 14 December 1996     

Fraktionierte Kristallisation von Ammonium- und Magnesiumdoppelnitraten der Ceriterden; Bestimmung der Trennfaktoren und Vergleich der Trennwirkung

Summary The Separation Factors for Pr/La, Nd/Pr, and Sm/Nd, characterizing the crystallization of ammonium and magnesium double nitrates under practical conditions, were determined analytically and are discussed. They confirm that La and Pr can be separated better by fractional crystallization of ammonium double nitrates, whereas in the presence of Sm the magnesium double nitrates are preferable.

     

Craig-Verteilung von Seltenerdnitraten im System Tri-n-butylphosphat—Salpetersäure, 3. Mitt.: Reindarstellung von Lanthan-, Praseodym- und Neodymoxid

Zusammenfassung Die präparativeCraig-Verteilung mit einer Apparatur von 80 Elementen ergab bei Entnahme der Oberphase aus angereicherten Oxiden (Einsatz 75 g) La₂O₃, Pr₆O₁₁ und Nd₂O₃ in Reinheiten zwischen 99,9 und 99,99% (Ausbeuten 80–85%); bis 437 Verteilungsstufen gelangten zur Wirkung.

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Craig distribution of rare earth nitrates in the system tri-n-butyl phosphate—nitric acid, III. Purification of lanthanum, praseodymium and neodymium oxides

PreparativeCraig distribution using an apparatus with 80 elements and withdrawal of upper phase starting with enriched oxides (input 75 g), gave La₂O₃, Pr₆O₁₁ and Nd₂O₃ in purities from 99.9 to 99.99% (80–85% yield); up to 437 stages were effective.

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Characteristic behavior of macro-, semimicro- and microelectrodes in voltammetric and chronoamperometric measurements

The advantages of microelectrodes such as the improvement of signal-to-noise ratio, the ability to perform electrochemical measurements in high resistive solutions and small RC-time constants give the possibility of an extended use for voltammetric and chronoamperometric techniques in analytical chemistry. In this comparative study, the microelectrode properties of three selected electrodes were examined. The characterization of a RAM-microarray electrode, an epoxy-impregnated carbon electrode and a conventional glassy carbon macroelectrode was performed by cyclic voltammetry at different scan rates, by DP-voltammetric measurements using different concentrations of supporting electrolyte and by transient measurements. It could be shown, that in comparison to the microarray electrode and to the glassy carbon macroelectrode, respectively, the results obtained by using the epoxy-impregnated carbon electrode are caused by its semimicroelectrode character.     

Series representation for semistable laws and their domains of semistable attraction

If the centered and normalized partial sums of an i.i.d. sequence of random variables converge in distribution to a nondegenerate limit then we say that this sequence belongs to the domain of attraction of the necessarily stable limit. If we consider only the partial sums which terminate atk _n wherek _n+1 ck _n then the sequence belongs to the domain of semistable attraction of the necessarily semistable limit. In this paper, we consider the case where the limiting distribution is nonnormal. We obtain a series representation for the partial sums which converges almost surely. This representation is based on the order statistics, and utilizes the Poisson process. Almost sure convergence is a useful technical device, as we illustrate with a number of applications.This research was supported by a research scholarship from the Deutsche Forschungsgemeinschaft (DFG).     

Synthesis and absolute configuration of clemastine and its isomers (author's transl)]

Synthesis and Absolute Configuration of Clemastine and its Isomers. Condensation of 4-chloro-α-methylbenzhydrylalkohol ( 1 ) with 2-(2-chloroethyl)-1-methylpyrrolidine ( 2 ) gave an isomeric mixture of 2-[2-(p-chloro-α-methyl-=-phenylbenzyloxy)ethyl]-1-methylpyrrolidine ( 3 ) and 4-(p-chloro-=-phenylbenzyloxy)-1-methyl-hexahydroazepin ( 4 ). The separation of the four possible optically active isomers of 3 is described and their absolute configuration established by degradation to (R)- and (S)-1-methyl-2-pyrrolidineethanol ( 6 ), respectively, and by an X-ray cristallographic analysis of the quarternary methiodide of the isomer 3-A . Clemastine (3-A) is (+)-(2R)-2-[2-((αR)-(p-chloro-α-methyl-α-phenylbenzyloxy)ethyl)]-1-methylpyrrolidine.