  We study the collisional properties of an ultracold mixture of cesium atoms
and dimers close to a Feshbach resonance near 550G in the regime of positive
$s$-wave scattering lengths. We observe an atom-dimer loss resonance that is
related to Efimov's scenario of trimer states. The resonance is found at a
value of the scattering length that is different from a previous observation at
low magnetic fields. This indicates non-universal behavior of the Efimov
spectrum for positive scattering lengths. We compare our observations with
predictions from effective field theory and with a recent model based on the
van der Waals interaction. We present additional measurements on pure atomic
samples in order to check for the presence of a resonant loss feature related
to an avalanche effect as suggested by observations in other atomic species. We
could not confirm the presence of such a feature.
