Fibring logics : the Portuguese School

Can we think of predicate temporal logic as resulting from a "combination operation" on first-order logic and propositionnal temporal logic ? Given two logics enjoying properties like completness, decidability, compactness etc., is there a systematic way to combine them in a new logic that enjoy these properties too (or : is it possible to find a way of caracterizing logic and then to define an operation of combining logics which have nice preservation properties? ) etc. Those questions have nice technical and philosophical aspects, and probably the best place to study them today is the IST - Instituto Superior Técnico, Lisboa, in The Center for Logic and Computation. Among distinguished members of the institute are A. Sernadas, C. Sernadas, W. Carnielli, or C. Caleiro.
For those interested in learning about these matters, let me mention three nice introductions to the subject of combining logic (especially fibring), both mathematically and philosophically motivated. Each of them extends its predecessors in the list, with overlap. The shorter one is Combining logic systems: Why, how, what for? (2003, 7 pages), and the second one is Fibring logics: Past, present and future (published in Artemov and al. (ed.) We Will Show Them: Essays in Honour of Dov Gabbay, 2005. 22 p.). The last one was published in the Handbook of Philosophical Logic (2nd Edition, volume 13, 2005. 61 p.) : Fibring of logics as a universal construction (available from the IST web site) .