  We present new results from the Disks@EVLA program for two young stars: CY
Tau and DoAr 25. We trace continuum emission arising from their circusmtellar
disks from spatially resolved observations, down to tens of AU scales, at
{\lambda} = 0.9, 2.8, 8.0, and 9.8 mm for DoAr25 and at {\lambda} = 1.3, 2.8,
and 7.1 mm for CY Tau. Additionally, we constrain the amount of emission whose
origin is different from thermal dust emission from 5 cm observations. Directly
from interferometric data, we find that observations at 7 mm and 1 cm trace
emission from a compact disk while millimeter-wave observations trace an
extended disk structure. From a physical disk model, where we characterize the
disk structure of CY Tau and DoAr 25 at wavelengths shorter than 5 cm, we find
that (1) dust continuum emission is optically thin at the observed wavelengths
and over the spatial scales studied, (2) a constant value of the dust opacity
is not warranted by our observations, and (3) a high-significance radial
gradient of the dust opacity spectral index, {\beta}, is consistent with the
observed dust emission in both disks, with low-{\beta} in the inner disk and
high-{\beta} in the outer disk. Assuming that changes in dust properties arise
solely due to changes in the maximum particle size (amax), we constrain radial
variations of amax in both disks, from cm-sized particles in the inner disk (R
< 40 AU) to millimeter sizes in the outer disk (R > 80 AU). These observational
constraints agree with theoretical predictions of the radial-drift barrier,
however, fragmentation of dust grains could explain our amax(R) constraints if
these disks have lower turbulence and/or if dust can survive high-velocity
collisions.
