Mathematical ences an international journal Volume 120 HEIN STIGUM, W. FALCK, AND P. MAGNus (Oslo, Norway) The Core Group Revisited: The Effect of Partner Mixing and Migration on the Spread of Gonorrhea, Chlamydia and HIV YUANHUA TANG AND HANS G. OTHMER (Salt Lake City, Utah) A G Protein-Based Model of Adaptation in Dictyostelium discoideum .... . .2: YANG KUANG (Tempe, Arizona) AND YASUHIRO TAKEUCHI (Hamamatsu, Japan) Predator—Prey Dynamics in Models of Prey Dispersal in Two-Patch Environments BERNARD DACOROGNA, FRANCOIS WEISSBAUM, AND ROGER ARDITI (Lausanne, Switzerland) Maximum Sustainable Yield with Continuous Age Structure and Density-Dependent Recruitment N. Hooke, C. S. HENRIQUEZ, P. LANZKRON, AND D. ROSE (Durham, North Carolina) Linear Algebraic Transformations of the Bidomain Equations: Penentnoms Hor Pepenertens BESEROGS «wc cece reer eesececceces NIKOLAUS BECKER AND WERNER RITTGEN (Heidelberg, Germany) Fitting Epidemiologic Follow-Up Studies with Cumulative Damage Models PETER R. JOHNSON, STEPHEN J. WALKER, JARI A. K. HYTTINEN, AND DAVID KILPATRICK (Hobart, Australia) Inverse Electrocardiographic Transformations: Dependence on the Number of Epicardial Regions and Body Surface Data Points NATALIA TRAYANOVA (Durham, North Carolina) An Approximate Solution on the Periodic Bidomain Equations in One Dimension ANNETTE Kopp-SCHNEIDER (Heidelberg, Germany) AND CHRISTOPHER J. PORTIER (Research Triangie Park, North Carolina) A Stem Cell Model for Carcinogenesis DANIEL ZELTERMAN, PATRICIA M. GRAMBSCH, CHAP T. LE, JENNIE Z. MA, AND JAMES W. CURTSINGER (Minneapolis, Minnesota) Piecewise Exponential Survival Curves with Smooth Transitions.........