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 A. Zadeh. Iranian cardiologist Tofigh Mussivand invented and developed the first artificial cardiac pump, the precursor of the artificial heart Furthering research and treatment of diabetes, the HbA1c was discovered by Samuel Rahbar. A substantial number of papers in string theory are published in Iran. Iranian American string theorist Kamran Vafa proposed the Vafa–Witten theorem together with Edward Witten. In August 2014, Iranian mathematician Maryam Mirzakhani became the first woman, as well as the first Iranian, to receive the Fields Medal, the highest prize in mathematics.