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Niels Bohr Institute: Mottelson was associated with the Niels Bohr Institute in Denmark. This institute is a world-renowned center for theoretical physics, established in 1921 by Niels Bohr, a Nobel laureate in physics. Mottelson conducted groundbreaking research at the institute, collaborating with Aage Bohr, the son of Niels Bohr. Their work on the collective model of the nucleus earned them the Nobel Prize in Physics in 1975.