This project is mathematical research in operator theory, a subject that had its origins in quantum mechanics (where operators on Hilbert space are used in place of scalars to represent physical quantities), but that has long since acquired a vigorous life of its own. The world of operators, being infinite-dimensional and noncommutative, is full of remarkable phenomena that are not present in the more familiar world of scalars. More specifically, Professor Herrero will work on problems related to compact perturbations and approximation of Hilbert space operators, including approximation by similarity - invariant classess of operators and closures of joint similarity orbits. He will also study the spectral structures of multicyclic operators.