i also applied to MIT DMSE and freaked out when i saw they have started to inform applicants of the outcomes..
i've heard from 2 schools in the past week, rejected by UIUC but got a positive response from Berkeley..
my stats are very similar to yours..
BS: GPA 3.7/4.0, 2 first authors papers is australian journal of chemistry and soft matter.
MS: research-based, 1 co-authored paper in Langmuir and submitted 2 more to langmuir and soft matter, respectively.
GRE: V590, Q790, AW3.5
from your stats, you seemed to have good reason for applying to those schools.. is UPenn your backup?
i'm sure you'll at least get into northwestern.. i contacted 2 Northwestern professors and they really liked that i have some publications too.. perhaps you've been let down a little by your AW.