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The present study is focused on international collaboration in science, involving more than two countries. The authors developed a promising model to measure and analyse the extent of multilateral co-authorship links in a previous study. The model is based on a series expansion approach which relates a new indicator, the Multilateral Collaboration Index (p), to the share of internationally co-authored papers (f). The model was found suitable to classify both the share of international papers, as well as the extent of multilateral links through the deviations from their expectations. A comparative analysis is made of changing collaboration patterns between 1983 and 1993 for 8 selected subfields, as well as all fields combined of the most active 38 countries. As expected an intensification of international scientific collaboration was observed, especially for a number of former COMECON countries. Different types of behaviour for different countries and science subfields emerged.

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We have found the exact ground state for a large class of antiferromagnetic spinone chains with nearest and next-nearest neighbour interactions. The ground state is characterized as a matrix product of local site states and has the properties characteristic of the Haldane scenario. * Work performed within the research program of the Sonderforschungsbereich 341, Köln-Aachen-Jülich

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