  Employing a short-range two-channel description we derive an analytic model
of atoms in isotropic and anisotropic harmonic traps at a Feshbach resonance.
On this basis we obtain a new parameterization of the energy-dependent
scattering length which differs from the one previously employed. We validate
the model by comparison to full numerical calculations for Li-Rb and explain
quantitatively the experimental observation of a resonance shift and
trap-induced molecules in exited bands. Finally, we analyze the bound state
admixture and Landau-Zener transition probabilities.
