Esther M. Conwell and Victor F. Weisskopf publish the first rigorous theoretical model of how electrons scatter upon colliding with ionized impurity atoms inside a semiconductor, explaining how charge-carrier mobility varies with temperature and doping level. The work, completed in 1943 but not published until 1950 due to various circumstances, transformed semiconductor design from an empirical trial-and-error process into a predictive science based on quantitative physical models, laying the theoretical groundwork that decades later would allow computer simulation of device behavior before manufacturing.