Robinson, James C.Vidal López, Alejandro2023-06-202023-06-202006-01-150022-039610.1016/j.jde.2005.04.009https://hdl.handle.net/20.500.14352/49662It is known that any periodic orbit of a Lipschitz ordinary differential equation must have period at least 2π/L, where L is the Lipschitz constant of f. In this paper, we prove a similar result for the semilinear evolution equation du/dt=-Au+f(u): for each α with 0 α 1/2 there exists a constant Kα such that if L is the Lipschitz constant of f as a map from D(Aα) into H then any periodic orbit has period at least KαL-1/(1-α). As a concrete application we recover a result of Kukavica giving a lower bound on the period for the 2d Navier–Stokes equations with periodic boundary conditions.engjournal articlehttp://www.sciencedirect.com/science/journal/00220396open access517.9Period orbitsMinimal periodSemilinear evolution equationsNavier–Stokes equationsEcuaciones diferenciales1202.07 Ecuaciones en Diferencias