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  • 1
    ISSN: 1432-2234
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Fulven, Azulen, zwei Hafnersche Kohlenwasserstoffe und Pleiadien werden mit Hilfe der verbesserten L.C.A.O.-Methode untersucht. Durch aufeinander folgende Versuche werden die π-Ladungen mit den effektiven atomaren Ladungen in Übereinstimmung gefunden, ebenso die benützten Bindungsabstände mit den durch Bindungsindex berechneten Abständen. Die berechneten Übergangsenergie stimmen mit dem Experiment ausgezeichnet überein. Die verschiedenen Versuche zeigen, daß eine gute Kohärenz für die Ladungen und die Abstände nötig ist. Eine neue Definition für die Aromatizität ist vorgeschlagen.
    Abstract: Abstract Molecules of Fulvene, Azulene, two Hafner's hydrocarbones and Pleiadiene are studied using the improved L.C.A.O. theory. Through successive trials, the π-electronic charges are coherent with the effective atomic charges and the interatomic distances with these obtained from bond order. The transition energies are in good agreement with the experiment. The various trials show that it is necessary to obtain a good coherence for charges and bond lengths. A new definition of Aromaticity is proposed.
    Notes: Résumé Le fulvène, l'azulène, deux hydrocarbures d'Hafner et le pléiadiène sont étudiés par la méthode L.C.A.O. améliorée. Par essais successifs les charges électroniques π sont en accord avec les charges effectives des orbitales atomiques et les distances interatomiques avec celles déduites des indices de liaison. Les énergies de transition sont en excellent accord avec l'expérience. Les divers essais effectués montrent la nécessité d'obtenir une bonne cohérence pour les charges et les distances. Une nouvelle définition de l'aromaticité est proposée.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2234
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Les différentes structures du pentalène, de l'heptalène et de l'azulène sont étudiées par la méthode L.C.A.O. améliorée. Les résultats relatifs aux chargesπ, aux énergies,π etσ, aux aromaticités, aux potentiels d'ionisation et aux énergies de transition conduisent à préférer les structuresC 2h aux structuresD 2h pour les molécules de pentalène et d'heptalène et la structureC 2v à la structureC s pour la molécule d'azulène.
    Abstract: Résumé Die verschiedenen Strukturen der Pentalen-, Heptalen- and Azulenmolekeln werden mit Hilfe der verbesserten LCAO-Methode untersucht. Die für dieπ- undσ-Energien, Aromatizität, Ionizations-und Übergangsenergien erhaltenen Ergebnisse zeigen, daß für Heptalen und Pentalen dieC 2h -Struktur in besserer Übereinstimmung mit dem Experiment ist als dieD 2h -Struktur. Dagegen stimmt für Azulen dieC 2v -Struktur besser als dieC s Struktur mit dem Experiment überein.
    Notes: Abstract The different structures of pentalene, heptalene and azulene are studied using the improved LCAO method. The results we got for theπ-electron densities,π andσ energies, aromaticity, ionisation potentials and transitions energies show that, for pentalene and heptalene theC 2h structure is better than theD 2h one and for azulene it is theC 2v structure who is better than theC s one.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 34 (1996), S. 1113-1125 
    ISSN: 0887-6266
    Keywords: polyethylene ; tensile necking ; plastic instability ; chain orientation ; strain hardening ; strain rate sensitivity ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The development of a plastic instability in a high-density ethylene-butene copolymer under tensile drawing was monitored by means of a video-controlled optical extensometer in order to study the mechanism of initiation and propagation of necking. True-stress true-strain curves measured along the neck at various times of the drawing are compared with the curve recorded as a function of time at the locus where the neck started. A strain rate gradient is shown to build up during the stage of neck initiation. Evidence is given of tensile normal stress in the concave part of the neck shoulder. X-ray diffraction reveals an oblique preferred orientation of the crystal c-axis that is governed by the lower energy-consuming pathway for the deformation. This is responsible for the plastic flow localization owing to an improved shear ability. The gradual c-axis orientation towards the draw direction as the neck grows involves a strain-hardening effect that leads to neck stabilization. The conclusion is put forward that neck propagation lies in the gradation of the preferred orientation along the neck shoulder rather than in stress triaxiality. Comparison with a parent low-density copolymer shows a better trend for oblique preferred orientation of the c-axis and a reduced propensity for localized plastic flow thanks to a more homogeneous distribution of the stress over the crystallites. © 1996 John Wiley & Sons, Inc.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
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