Iranian scientists outside Iran have also made some major contributions to science. In 1960, Ali Javan co-invented the first gas laser, and fuzzy set theory was introduced by Lotfi Zadeh. Iranian cardiologist, Tofy Mussivand invented and developed the first artificial cardiac pump, the precursor of the artificial heart. Furthering research and treatment of diabetes, HbA1c was discovered by Samuel Rahbar. Iranian physics is especially strong in string theory, with many papers being published in Iran. Iranian-American string theorist Kamran Vafa proposed the Vafa-Witten theorem together with Edward Witten. In August 2014, Maryam Mirzakhani became the first-ever woman, as well as the first-ever Iranian, to receive the Fields Medal, the highest prize in mathematics.