Das papierchromatographische Verhalten und den Nachweis zahlreicher Phenolk?rper

Ohne Zusammenfassung     

Justification of the Mmataga-Nishimoto approximation

Coulson's expression for the two-centre Coulombic integral, (pp/qq), obtained by use of Saturno's operator, is shown to yield values almost identical to those given by the empirical relationship of Mataga and Nishimoto.     

SCF-π-electron calculations using orthogonalised atomic orbitals

SCF-LCAO--electron calculations are made for a number of representative hydrocarbon systems by a non-empirical variant of the Adams-Miller technique. The essential modifications introduced are: - (i) the determination of the H ⁰ parameters by direct calculation instead of from experimental data, and (ii) the use of a properly orthogonalised set of electron repulsion integrals. Results are considered for two different values of the one-centre repulsion integral, (pp/pp): — (a) using 11.13 eV, as derived from (pp/pp)=I-A, and (b) using 9.82 eV, as given by direct calculation with Saturno's operator. The latter is found overall to give significantly better values for singlet state excitation energies, and these compare quite favourably with the results of semi-empirical methods. The need for the explicit calculation of all penetration integral terms occurring in the H ⁰ parameters is demonstrated, and the dependence of the results on the assumed value of Z investigated. Variations arising from the choice of hydrogenic or Slater-type 2s orbitals for evaluating the penetration integrals are described.

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Zusammenfassung Für eine Anzahl repräsentativer Kohlenwasserstoffsysteme werden mit Hilfe einer nicht-empirischen Variante der Adams-Miller-Technik SCF-LCAO--Elektronenrechnungen durchgeführt. Dabei werden im wesentlichen folgende Änderungen vorgenommen: (i) Die Bedingung des H ⁰-Parameters erfolgt durch direkte Berechnung und nicht aus experimentellen Daten. (ii) Es wird ein geeignet orthogonalisierter Satz an Elektronenwechselwirkungsintegralen benutzt. Die Ergebnisse werden für zwei verschiedene Werte des Einzentrenwechselwirkungsintegrals (pp/pp) diskutiert: (a) Aus der Beziehung (pp/pp) =I-A erhält man für (pp/pp) den Wert 11,13eV. (b) Die direkte Berechnung mit Saturno's Operator ergibt für (pp/pp) einen Wert von 9,82 eV. Mit dem letzten Wert erhält man wesentlich bessere Werte für die Anregungsenergien einfach angeregter Zustände und überaus gute Über-einstimmung mit den Ergebnissen semi-empirischer Methoden. Die Möglichkeit einer expliziten Berechnung aller Überlappungsintegrale, die in dem H ⁰- Parameter enthalten sind, wird gezeigt und die Abhängigkeit der Ergebnisse von dem angenommenen Z-Wert untersucht. Unterschiede, die durch die Wahl von Wasserstoff-oder Slater-Typ-2s-Funktionen für die Berechnung der Überlappungsintegrale entstehen, werden dargestellt.

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Résumé On effectue des calculs SCF-LCAO sur les systèmes d'un certain nombre d'hydrocarbures représentatifs dans une version non empirique de la technique de Adams-Miller. Les principales modifications introduites sont (i) la détermination des paramètres de H ⁰ par un calcul direct au lieu de l'utilisation de données expérimentales; (ii) l'utilisation d'un jeu convenablement orthogonalizé d'intégrales de répulsion électronique.On considère les résultats pour 2 valeurs différentes de l'intégrale de répulsion monocentrique (pp/pp): (a) 11.13 eV, déduite de la formule (pp/pp)=I-A et (b) 9,82 eV, déduite du calcul direct par l'opérateur de Saturno. Cette dernière valeur donne au total des valeurs nettement meilleures des énergies de transition singulet, qui se comparent assez bien avec les résultats des méthodes semiempiriques. On démontre la nécessité du calcul explicite de toutes les intégrales de pénétration qui interviennent dans les paramètres H ⁰. On analyse la dépendance des résultats á la valeur adoptée pour Z. On décrit l'influence du choix d'orbitales 2s hydrogenoïdes ou du type Slater sur l'évaluation des intégrales de pénétration.

     

Refractive-index profiling of optical fibers with axial symmetry by use of quantitative phase microscopy

The application of quantitative phase microscopy to refractive-index profiling of optical fibers is demonstrated. Phase images of axially symmetric optical fibers immersed in index-matching fluid are obtained, and the inverse Abel transform is used to obtain the radial refractive-index profile. This technique is straightforward, nondestructive, repeatable, and accurate. Excellent agreement, to within approximately 0.0005, between this method and the index profile obtained with a commercial profiler is obtained.     

A sampling and analytical methodology for dental trace element analysis

The role of trace elements in human health and environmental pollution has developed into an extensive field of research. This study describes a sampling and analytical strategy to determine the trace element content of primary (deciduous) teeth and to assess their use in environmental health and nutrition studies. Exfoliated and extracted primary teeth were collected from 21 Ugandan and 27 UK children. The crown and root of the teeth were separated and the former digested and analysed for several elements by inductively coupled plasma mass spectrometry. The influence of country, tooth type, age and gender were statistically investigated in addition to within-person variation. A principal components analysis (PCA) was used to treat the data in a multivariate fashion and facilitated the moderation of outliers. The results demonstrated that country of origin has an important influence on the elemental composition of teeth and that tooth type should be controlled in these types of studies. Given such a restriction, the age and gender of the donor should have no effect and do not need to be controlled. In addition, where country of domicile, age and gender were controlled, the concentrations of most elements within a single tooth type were representative of an individual and therefore may be indicative of health status.     

Taut Foliations in Punctured Surface Bundles, II

Given a fibered 3-manifold M, we investigate exactly which boundaryslopes can be realized by perturbing fibrations along productdiscs. Since these perturbed fibrations cap off to give tautfoliations in the corresponding surgery manifolds, we obtainsurgery information. For example, recall that a knot k is saidto satisfy Property P if no finite surgery along k yields asimply-connected 3-manifold. We show that if a non-trivial fiberedknot k S³ fails to satisfy Property P, then necessarily k ishyperbolic with degeneracy slope . When k is hyperbolic and (respectively, ), we show that the only candidate for a counterexample to Property P is surgery coefficient (respectively, . 2000 Mathematical Subject Classification: primary57M25; secondary 57R30.     

Chiral amplification by polypeptides and its relevance to prebiotic catalysis

Polyleucine prepared from scalemic Leu-NCA monomers, shows high chiral amplification in the Julia-Colonna epoxidation of chalcone.     

The isomerisation of (Z)-3-[2H1]-phenylprop-2-enone as a measure of the rate of hydroperoxide addition in Weitz-Scheffer and Julia-Colonna epoxidations

(Z)-3-[2H1]-Phenylprop-2-enone is isomerised by hydroperoxide to an equimolar mixture of the (Z)- and (E)-isomers prior to epoxidation. Poly-(L)-leucine (10 mole %) accelerates the addition of hydroperoxide by an order of magnitude and sequesters hydroperoxide from THF.