“…We mention here that fractional derivatives appear in many engineering problems. They arise naturally in many fields such as in probability, physics, astrophysics, chemical physics, anomalous diffusion, seismic analysis, finance, optic and signal processing, robust control, electromagnetism, biology, viscoelasticity, acoustics (see [12,15,21,22,23] to cite but a few). In mechanics, for instance, fractional derivatives are more adequate to model the damping than the usual frictional or structural dampings (described by the time derivative of order one or the time derivative of the Laplacian, respectively).…”