  We visualize entanglements in polymer melts using molecular dynamics
simulation. A bead at an entanglement interacts persistently for long times
with the non-bonded beads (those excluding the adjacent ones in the same
chain). The interaction energy of each bead with the non-bonded beads is
averaged over a time interval $\tau$ much longer than microscopic times but
shorter than the onset time of tube constraints $\tau_{\rm e}$. Entanglements
can then be detected as hot spots consisting of several beads with relatively
large values of the time-averaged interaction energy. We next apply a shear
flow with rate much faster than the entangle motion. With increasing strain the
chains take zigzag shapes and a half of the hot spots become bent. The chains
are first stretched as a network but, as the bends approach the chain ends,
disentanglements subsequently occur, leading to stress overshoot observed
experimentally.
