vi The intent, therefore, was to provide for a fresh and original review of all relevant topics and issues in the field, following a comprehensive and coherent programme. Such an ambitious goal could only be reached thanks to the unlimited collaboration of the lecturers: They were requested to produce nothing less than "freer, broader, speculative and personal "considerations of the subjects" they had to cover ••• And so they did: their presentations unfolded a fantastic picture, a most fascinating and meaningful identification of the field, its present problems and trends. But participants at this conference contributed many valuable observations while discussing specific points. Unfortunately, more often than not, it proved impossible to identify them in the records. Accordingly, we incorporated here and there some of these "anonymous" contributions as part of the edited version of the texts. To all of the participants, I would like to express my gratitude for their actively taking part in all the scientific (and social ••• ) activities (lectures, round tables, posters, encounters) of this N.A.T.O. ASl. The result was a stimulating atmosphere, conducive to authentic scientific exchanges. Hence, the success of this meeting should be credited only to them. Finally, on behalf of all participants, I would like to thank Professor Sissini, the Mayor of Maratea, and Mr. B. Vitolo, the Chairman of its Tourist Office: their enthusiastic support greatly contributed to make of our time in their wonderful seaside resort an unforgettable one.