Iran's scientific progress is subject to many problems including funding, international sanctions, and management. However, in some areas such as medicine, surgery, pharmacology, stem cell research and theoretical physics (e.g. string theory), Iranian scientists have found international reputation since the Iranian revolution. Nuclear technology and stem cell research were the two fields that have enjoyed special support from the central government and Iranian leadership since the revolution. In 2005 Iran's national science budget was less than $1 billion and had not been subject to any significant increase since 15 years ago. But according to Science-Metrix, since 1990 Iran's scientific production has had a rapid buildup, and Iran currently has the fastest growth rate in science and technology worldwide. Iran is among the international leaders of stem cell technology and was the 10th country to produce embryonic human stem cells, although in terms of articles per capita basis, it reportedly ranked 16th in the world. Ayatollah Khomeini was the ruler of (or at least dominant figure in) Iran for a decade, from the founding of the Islamic Republic in April 1979 until his death in mid-1989. During that time the revolution was being consolidated as a theocratic republic under Khomeini, and Iran was fighting a costly and bloody war with Iraq. The Islamic Republic of Iran began with the Iranian Revolution. The first major demonstrations to overthrow Shah Mohammad Reza Pahlavi began in January 1978. The new theocratic Constitution — whereby Khomeini became Supreme Leader of the country — was approved in December 1979. In between, the Shah fled Iran in January 1979 after strikes and demonstrations paralyzed the country, and on February 1, 1979, Ayatollah Khomeini returned to Tehran to a greeting by several million Iranians. The final collapse of the Pahlavi dynasty occurred shortly after on February 11 when Iran's military declared itself "neutral" after guerrillas and rebel troops overwhelmed troops loyal to the Shah in armed street fighting. Iran officially became the Islamic Republic on April 1, 1979, when Iranians overwhelmingly approved a national referendum to make it so. The initial impact of the Islamic revolution around the world was tremendous. In the non-Muslim world it has changed the image of Islam, generating much interest in the politics and spirituality of Islam, along with "fear and distrust towards Islam" and particularly the Islamic Republic and its founder. In the Mideast and Muslim world, particularly in its early years, it triggered enormous enthusiasm and redoubled opposition to western intervention and influence. Islamist insurgents rose in Saudi Arabia (the 1979 week-long takeover of the Grand Mosque), Egypt (the 1981 machine-gunning of the Egyptian President Sadat), Syria (the Muslim Brotherhood rebellion in Hama), and Lebanon (the 1983 bombing of the American Embassy and French and American peace-keeping troops).