"Perturbation theory." . . "Wave propagation." . . . . . . "Interactions of elastic waves in solids"@en . "Interactions of elastic waves in solids" . . . . . . . . . . . . . . . . . . . . . "INTERACTIONS OF ELASTIC WAVES IN SOLIDS"@en . . . "Solids." . . "MASSACHUSETTS INST OF TECH CAMBRIDGE." . . "Phonons." . . "Roosterdynamica." . . "Single crystals." . . "Mathematical analysis." . . "Quantum theory." . . "Fononen." . . . .