Complex sentence: Lewin then participated in the beginnings of laboratory training, or T-groups, and, after his death in 1947, his close associates helped to develop survey-research methods at the University of Michigan.
Split into simpler sentences: Lewin then participated in the beginnings of laboratory training, or T-groups. After Lewin's death in 1947, his close associates helped to develop survey-research methods at the University of Michigan.