Kalorimetrische Untersuchungen des Wassereinflusses auf den Lösungsvorgang von Aerosol OT in apolaren Lösungsmitteln

Calorimetric Investigations of the Effect of Water on the Solution Process of Aerosol OT in Apolar Media. Heats of solution of Aerosol OT in apolar solvents are influenced considerably by already small amounts of water. Calorimetric investigations of the solution process with differently dried surfactant and solvent samples showed the predominating effect on the heats of hydration with regard to the ionic and polar groups of the surfactant. Only if the hydration is finished prior to the process of solution, the latter is endothermic. An estimation of the various enthalpic contributions demonstrates that the destruction of the coherence of the built-in water within the surfactant is decisive in the latter case. Two models corresponding to definite structures of the liquid crystalline mesophase of the surfactant show very satisfactory agreement with the experimental ΔH-values.     

Some perfect coloring properties of graphs

A Grundy n-coloring of a finite graph is a coloring of the points of the graph with the non-negative integers smaller than n such that each point is adjacent to some point of each smaller color but to none of the same color. The Grundy number of a graph is the maximum n for which it has a Grundy n-coloring. Characterizations are given of the families of finite graphs G such that for each induced subgraph H of G: (1) the Grundy number of H is equal to the chromatic number of H; (2) the Grundy number of H is equal to the maximum clique size of H; (3) the achromatic number of H is equal to the chromatic number of H; (4) the achromatic number of H is equal to the maximum clique size of H. The definitions are further extended to infinite graphs, and some of the above characterizations are shown to be true for denumerable graphs and locally finite graphs.     

On the nitration of 2-pyrone

A 1:1 adducl of 2-pyrone and nitronium fluoroborate has been delected by nmr and is a possible precursor of 5-nitro-2-pyrone, a subsequently formed product. From comparison of the nmr spectra of the 1:1 adduct and 2-methoxypyrylium fluoroborate, the adduct is believed to be the pyrylium fluoroborate derived from nitration of the carbonyl oxygen of 2-pyrone.     

NMR spectra of 2-pyrone and 2-pyrone derivatives

An analysis of the complex NMR spectrum of 2-pyrone is presented and the spectra of a series of variously substituted 2-pyrones and 5,6-dihydro-2-pyrones are discussed. It is demonstrated that NMR spectroscopy affords a convenient and reliable method of assigning the position of substituents on the 2-pyrone nucleus.     

Antiferroelectric behavior in symmetric KNbO(3)/KTaO(3) superlattices

Antiferroelectric behavior is observed in artificially layered KTaO (3)/KNbO (3) perovskite superlattices. While KTaO (3) and KNbO (3) are ferroelectric and paraelectric, respectively, the superlattice appears antiferroelectric based on an increase in the dielectric constant with applied dc bias. This dielectric behavior is inconsistent with the nonlinear response for either paraelectric or ferroelectric materials. However, an increase in the dielectric constant with applied electric field is consistent with antiferroelectric behavior. The antiferroelectric ordering appears to be induced by cation modulation imposed by the superlattice.     

Study of factors influencing pressurised solvent extraction of polar steroids from plant material. Application to the recovery of withanolides

Summary Pressurised solvent extraction was applied to the extraction of three withanolides from the leaves oflochroma gesnerioides. A study was carried out of the influence of various parameters on the extraction efficiency and kinetic parameters; these included the nature of the extracting solvent, its flow rate, the pressure and temperature, as well as the particle size of the plant material. The pressurised solvent extraction method compared to a conventional Soxhlet extraction showed similar recoveries and extraction selectivity but the total handling time and solvent volume were dramatically reduced.     

Mellin‐edge representations of elliptic operators

We construct a class of elliptic operators in the edge algebra on a manifold M with an embedded submanifold Y interpreted as an edge. The ellipticity refers to a principal symbolic structure consisting of the standard interior symbol and an operator‐valued edge symbol. Given a differential operator A on M for every (sufficiently large) s we construct an associated operator ??_s in the edge calculus. We show that ellipticity of A in the usual sense entails ellipticity of ??_s as an edge operator (up to a discrete set of reals s). Parametrices P of A then correspond to parametrices ??_s of ??_s, interpreted as Mellin‐edge representations of P. Copyright © 2005 John Wiley & Sons, Ltd.     

Is water critical to the formation of micelles in apolar media??

Photon correlation studies in H₂O/sodium di-2-ethylhexylsulfosuccinate (AOT)/i-C₈H₁₈-systems, pertinent IR. investigations, and vapor pressure osmometric measurements with alkylated quaternary ammonium di-2-ethylhexylsulfosuccinates strongly suggest water to be pre-requistite for the micellization in apolar media.     

Collectivity in neutron-deficient Pb and Po nuclei

Lifetimes of low-lying yrast states in ¹⁸⁶Pb and ¹⁹⁴Po have been determined by employing, for the first time, the recoil-decay tagging technique in recoil distance Doppler-shift lifetime measurements. In addition, lifetime measurements of prolate states in ¹⁸⁸Pb up to the 8⁺ state were carried out using the recoil gating method. The deformation parameters and for the prolate (^186,188Pb) and the oblate (¹⁹⁴Po) bands, respectively, have been extracted from the measured lifetimes. 27.70.+q–