In this three-year U.S.-Yugoslav cooperative research project in solid state physics between Ljiljana Dobrosavljevic of the Institute of Physics in Belgrade and John Clem of Iowa State University, the investigators will develop a phenomenological theory of magnetic and transport properties of high tc superconductors. Through these studies, the investigators will identify the mechanism for superconductivity (how does it work), weak links in the materials, and inhibitors to electrical flow. Despite the significant advances in this field, experimentalists are searching for explanations to these problems. The U.S. and Yugoslav investigators are among the leaders in theoretical research. Their joint research will yield new insights into high tc superconducting properties and microstructure. This project was approved by the U.S.-Yugoslav Joint Board on Cooperation in Science and Technology and is supported through a joint fund consisting of matching contributions from the governments of the United States and Yugoslavia. The U.S. contribution is provided annually by the Department of State. No NSF funds are involved. Grants are made to the principal scientific institution in Yugoslavia, but include dollar funds for U.S. scientist travel to Yugoslavia and for Yugoslav scientists' living expenses in the U.S.