Mean curvature flow singularities for mean convex surfaces

We study the evolution by mean curvature of a smooth n-dimensional surface M subset of Rn+1, compact and with positive mean curvature. We first prove an estimate on the negative part of the scalar curvature of the surface. Th en we apply this result to study the formation of singularities by rescalin g techniques, showing that there exists a sequence of rescaled flows conver ging to a smooth limit flow of surfaces with nonnegative scalar curvature. This gives a classification of the possible singular behaviour for mean con vex surfaces in the case n = 2.