sentences:  From 1924 to 1930 he worked as an electrical engineer in the research laboratory of Westinghouse Electric (1886) in Pittsburgh.There under the influence of Stephen P. Timoshenko, who took him as his assistant, he began to study electrical and mechanical vibrations.At the same time, he attended night classes in Mathematics at the University of Pittsburgh, where he became an authority in problems on mechanics and vibration and received a doctorate in 1939.