Quantum mechanical tunneling across smooth double barrier potentials modeled
using Gaussian functions, is analyzed numerically and by using the WKB
approximation. The transmission probability, resonances as a function of
incident particle energy, and their dependence on the barrier parameters are
obtained for various cases. We also discuss the tunneling time, for which we
obtain generalizations of the known results for rectangular barriers.Comment: 23 pages, 8 figures, a slightly reduced version to appear in American
Journal of Physics, references correcte