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Inégalités isopérimétriques et applications Annales scientifiques de l'É.N.S. 4 e série, tome 15, n o 3 (1982), p. 513-541 © Gauthier-Villars (Éditions scientifiques et médicales Elsevier), 1982, tous droits réservés. L'accès aux archives de la revue « Annales scientifiques de l'É.N.S. » (http://www. elsevier.com/locate/ansens) implique l'accord avec les conditions générales d'utilisation (http://www.numdam.org/conditions). Toute utilisation commerciale ou impression systématique est constitutive d'une infraction pénale. Toute copie ou impression de ce fichier doit contenir la présente mention de copyright. Article numérisé dans le cadre du programme Numérisation de documents anciens mathématiques http://www.numdam.org/

The online search activities described here were conducted to provide environmental scientists with literature to use in their review of pesticide chemicals for regulatory decisions. The first criterion for this data gathering process was to have complete coverage to approach 100% recall of the papers published on the pesticide in question. As new databases were developed and current ones were updated, the number of searchable files multiplied. Running large profiles against each data‐base now resulted in, increased online costs, (connect‐time/print charges), greater overlap and duplication and, inundating the reviewer with thousands of citations. Thus it became apparent that the effectiveness of searching this multitude of applicable databases must be evaluated. Where is the overlap? Which data‐bases contain unique citations? How can the number of databases be decreased without minimizing the percentage of coverage?

Abstract. We introduce snowballs, which are compact sets in R 3 homeomorphic to the unit ball. They are 3-dimensional analogs of domains in the plane bounded by snowflake curves. For each snowball B a quasiconformal map f : R 3 → R 3 is constructed that maps B to the unit ball.

Abstract. Douady and Hubbard introduced the operation of mating of polynomials. This identifies two filled Julia sets and the dynamics on them via external rays. In many cases one obtains a rational map. Here the opposite question is tackled. Namely we ask when a given (postcritically finite) rational map f arises as a mating. A sufficient condition when this is possible is given. If this condition is satisfied, we present a simple explicit algorithm to unmate the rational map. This means we decompose f into polynomials, that when mated yield f . Several examples of unmatings are presented.