  In the First Part of this paper [that was submitted for pub. in 1991 and
appeared in print in Phys. Reports 214 (1992) 339] we critically review the
main theoretical definitions and calculations of the sub-barrier tunnelling and
reflection times. Moreover, within conventional QM, we propose a new definition
of such durations, on the basis of a recent general formalism of ours. At last,
we discuss a surprising result: that QM predicts tunnelling through opaque
barriers to take place with Superluminal group-velocities. In the Second Part
[that appeared in print later, in J. de Physique-I 5 (1995) 1351] we, e.g.,
present the results of some numerical calculations (based on our equations) on
the penetration and return times during tunnelling INSIDE a rectangular
potential barrier, and set forth suitable definitions also of the variances, or
dispersions, for the transmission and reflection time-durations. The numerical
evaluations confirm that our approach implied, and implies, the existence of
Superluminal tunnelling (that we called "Hartman effect"): an effect that in
these days is receiving --at Cologne, Berkeley, Florence and Vienna-- indirect,
but interesting, experimental verifications. More detailed reviews of the same
topics are in the LANL Archive cond-mat/9802126 (and in an Appendix to
physics/9712051, where the data are summarized of the experiments that --in
four different sectors of physics-- seem to indicate the existence of
Superluminal motions).
